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Indicators of Intrinsic Active Galactic Nucleus Luminosity: A Multi-wavelength Approach
Active galactic nuclei (AGNs) consist of an accretion disk around asupermassive black hole which in turn is surrounded by an obscuringtorus of dust and gas. As the resulting geometry of this system affectsthe observable properties, quantifying isotropic indicators of intrinsicAGN luminosity is important in selecting unbiased samples of AGNs. Inthis paper, we consider five such proxies: the luminosities of the [OIII]?5007 line, the [O IV]25.89 ?m line, the mid-infrared(MIR) continuum emission by the torus, and the radio and hard X-ray (E> 10 keV) continuum emission. We compare these different proxiesusing two complete samples of low-redshift Type 2 AGNs selected in ahomogeneous way based on different indicators: an optically selected [OIII] sample and an MIR-selected 12 ?m sample. To assess the relativemerits of these proxies, we have undertaken two analyses. First, weexamine the correlations between all five different proxies, and findbetter agreement for the [O IV], MIR, and [O III] luminosities than forthe hard X-ray and radio luminosities. Next, we compare the ratios ofthe fluxes of the different proxies to their values in unobscured Type 1AGNs. The agreement is best for the ratio of the [O IV] and MIR fluxes,while the ratios of the hard X-ray to [O III], [O IV], and MIR fluxesare systematically low by about an order of magnitude in the Type 2AGNs, indicating that hard X-ray-selected samples do not represent thefull Type 2 AGN population. In a similar spirit, we compare differentoptical and MIR diagnostics of the relative energetic contributions ofAGN and star formation processes in our samples of Type 2 AGNs. We findgood agreement between the various diagnostic parameters, such as theequivalent width of the MIR polycyclic aromatic hydrocarbon features,the ratio of the MIR [O IV]/[Ne II] emission lines, the spectral indexof the MIR continuum, and the commonly used optical emission-lineratios. Finally, we test whether the presence of cold gas associatedwith star formation leads to an enhanced conversion efficiency of AGNionizing radiation into [O III] or [O IV] emission. We find that nocompelling evidence exists for this scenario for the luminositiesrepresented in this sample (L bol ?109 –8 × 1011 L sun).
| XMM-Newton Observations of the Radio-Loud Broad Absorption Line Quasar FBQS J131213.5+231958
We present XMM-Newton observations of the broad absorption line (BAL)quasar FBQS J131213.5+231958. The X-ray spectrum of the source can bewell described by an absorbed power-law model in which the absorber iseither ionized or only partially covers the continuum source. This canexplain the apparent lack of absorption observed in the Chandra spectrumwith low signal-to-noise ratio. While the power-law slope of thespectrum is similar to that of non-BAL radio-loud quasars, the Eddingtonluminosity ratio is likely to be significantly higher than the mean.This shows that in high-mass black holes (BHs), high Eddington accretionmay not result in as steep of a spectrum as in lower-mass BHs. Thisprovides important constraints for accretion disk models. It alsoprovides support to the idea that BAL quasars, at least their radio-loudsubclass, represent an early evolutionary stage of quasars.
| First Views of a Nearby LIRG: Star Formation and Molecular Gas in IRAS 04296+2923
We present a first look at the local luminous infrared galaxy (LIRG)IRAS 04296+2923. This barred spiral galaxy, overlooked because of itslocation behind the Taurus molecular cloud, is among the half dozenclosest (D = 29 Mpc) LIRGs. More IR-luminous than either M82 or theAntennae, it may be the best local example of a nuclear starburst causedby bar-mediated secular evolution. We present Palomar J and Pa ?images, Very Large Array continuum maps from ?= 20-1.3 cm, asubarcsecond Keck Long Wavelength Spectrometer image at 11.7 ?m andOwens Valley Millimeter Array CO(1-0), 13CO(1-0), and 2.7 mmcontinuum images. The J-band image reveals a symmetric barred spiralgalaxy. Two bright, compact mid-infrared and radio sources in thenucleus mark a starburst that is energetically equivalent to~105 O7 stars, separated by lsim50 pc. This is probably apair of young super star clusters, with estimated stellar masses of~107 M sun each. The nuclear starburst is formingstars at the rate of ~12 ± 6 M sunyr-1, or about half of the total star formation ratefor the galaxy of ~25 ± 10 M sunyr-1. IRAS 04296+2923 is very bright in CO, and amongthe most gas-rich galaxies in the local universe. The 12COluminosity of the inner half kpc is equivalent to that of the entireMilky Way. While the most intense CO emission is extended over a 15'' (2kpc) diameter region, the nuclear starburst is confined to within1''-2'' (150-250 pc) of the dynamical center. Based on masses obtainedwith 13CO, we find that the CO conversion factor in thenucleus is lower than the Galactic value, X Gal COby a factor of three to four, typical of gas-rich spiral nuclei. Thenuclear star formation efficiency (SFE) isnucMgas/SFRnuc = 2.7 ×10-8yr-1, corresponding to a gasconsumption timescale, ?nuc SF ~ 4 ×107 yr. The SFE is 10 times lower in the disk, with?disk SF ~ 3.3 × 108 yr. Thelow absolute SFE in the disk implies that the molecular gas is notcompletely consumed before it drifts into the nucleus, and is capable offueling a sustained nuclear starburst. IRAS 04296+2923 appears to bebeginning a 100 Myr period as an LIRG, during which it will turn much ofits 6 × 109 Msun of molecular gas into anuclear cluster of stars.
| Modeling the Outflow in the Narrow-line Region of Markarian 573: Biconical Illumination of a Gaseous Disk
We present a study of the outflowing ionized gas in the resolvednarrow-line region of the Seyfert 2 galaxy Mrk 573, and its interactionwith an inner dust/gas disk, based on Hubble Space Telescope (HST) WideField Planetary Camera 2 and Space Telescope Imaging Spectrographobservations. From the spectroscopic and imaging information, wedetermined the fundamental geometry of the outflow and inner disk, viatwo modeling programs used to recreate the morphology of these regionsimaged with HST. We also determined that the bicone of ionizingradiation from the active galactic nucleus intersects with the innerdisk, illuminating a section of the disk including inner segments ofspiral arms, fully seen through structure mapping, which appear to beoutflowing and expanding. In addition, we see high velocities atprojected distances of >=2'' (~700 pc) from the nucleus, which couldbe due to rotation or in situ acceleration of gas off the spiral arms.We find that the true half-opening angle of the ionizing bicone(53°) is much larger than the apparent half-opening angle (34°)due to the above geometry, which may apply to a number of other Seyfertsas well.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555.
| Supermassive black holes do not correlate with galaxy disks or pseudobulges
The masses of supermassive black holes are known to correlate with theproperties of the bulge components of their host galaxies. In contrast,they seem not to correlate with galaxy disks. Disk-grown `pseudobulges'are intermediate in properties between bulges and disks; it has beenunclear whether they do or do not correlate with black holes in the sameway that bulges do. At stake in this issue are conclusions about whichparts of galaxies coevolve with black holes, possibly by being regulatedby energy feedback from black holes. Here we report pseudobulgeclassifications for galaxies with dynamically detected black holes andcombine them with recent measurements of velocity dispersions in thebiggest bulgeless galaxies. These data confirm that black holes do notcorrelate with disks and show that they correlate little or not at allwith pseudobulges. We suggest that there are two different modes ofblack-hole feeding. Black holes in bulges grow rapidly to high masseswhen mergers drive gas infall that feeds quasar-like events. Incontrast, small black holes in bulgeless galaxies and in galaxies withpseudobulges grow as low-level Seyfert galaxies. Growth of the former isdriven by global processes, so the biggest black holes coevolve withbulges, but growth of the latter is driven locally and stochastically,and they do not coevolve with disks and pseudobulges.
| The Redshift Search Receiver 3 mm Wavelength Spectra of 10 Galaxies
The 3 mm wavelength spectra of 10 galaxies have been obtained at theFive College Radio Astronomy Observatory using a new, very broadbandreceiver and spectrometer, called the Redshift Search Receiver (RSR).The RSR has an instantaneous bandwidth of 37 GHz covering frequenciesfrom 74 to 111 GHz and has a spectral resolution of 31 MHz (~100 kms-1). During tests of the RSR on the FCRAO 14 mtelescope the complete 3 mm spectra of the central regions of NGC 253,Maffei 2, NGC1068, IC 342, M82, NGC 3079, NGC 3690, NGC 4258, Arp 220,and NGC 6240 were obtained. Within the wavelength band covered by theRSR, 20 spectral lines from 14 different atomic and molecular specieswere detected. Based on simultaneous fits to the spectrum of eachgalaxy, a number of key molecular line ratios are derived. A simplemodel which assumes the emission arises from an ensemble of Milky Waylike Giant Molecular Cloud cores can adequately fit the observed lineratios using molecular abundances based on Galactic molecular cloudcores. Variations seen in some line ratios, such as 13CO/HCNand HCO+/HCN, can be explained if the mean density of themolecular gas varies from galaxy to galaxy. However, NGC 3690, NGC 4258,and NGC 6240 show very large HCO+/HCN ratios and requiresignificant abundance enhancement of HCO+ over HCN, possibledue to the proximity to active galactic nucleus activity. Finally, themass of dense molecular gas is estimated and we infer that 25%-85% ofthe total molecular gas in the central regions of these galaxies musthave densities greater than 104 cm-3.
| An Ultraviolet Spectroscopic Atlas of Local Starbursts and Star-forming Galaxies: The Legacy of FOS and GHRS
We present 46 rest-frame ultraviolet (UV) spectra of 28 local starburstand star-forming galaxies which were observed with the Faint ObjectSpectrograph (FOS) and the Goddard High Resolution Spectrograph (GHRS)of the Hubble Space Telescope (HST) at a spectral resolution of a few100 km s–1. We compare the HST spectra with lowerresolution International Ultraviolet Explorer (IUE) spectra of the samegalaxies and find systematic differences: the bright star clusterstargeted in HST's ~1'' apertures provide about 15% of the starburstluminosity traced by IUE's 10'' × 20'' aperture; they are bluerand have stronger stellar-wind features suggesting that the HSTapertures have preferentially been placed on the youngest areas of theburst. In contrast, lines arising from the interstellar medium (ISM)show similar equivalent widths in both the large and small apertureobservations, suggesting similar ISM properties from larger to smallerscales. In order to quantify the UV spectral morphology of star-forminggalaxies, we created a set of UV line indices similar to the standardoptical Lick indices. We discuss the relation between the UV spectralmorphology and the properties of the galaxy host. We present our atlasof FOS and GHRS spectra both in print and online. The data set is usefulas a baseline for comparisons with observations of the rest-frame UVspectra of star-forming galaxies at high redshift.
| The Great Observatories All-sky LIRG Survey: Comparison of Ultraviolet and Far-infrared Properties
The Great Observatories All-sky LIRG Survey (GOALS) consists of acomplete sample of 202 luminous infrared galaxies (LIRGs) selected fromthe IRAS Revised Bright Galaxy Sample (RBGS). The galaxies span the fullrange of interaction stages, from isolated galaxies to interacting pairsto late stage mergers. We present a comparison of the UV and infraredproperties of 135 galaxies in GOALS observed by GALEX and Spitzer. Forinteracting galaxies with separations greater than the resolution ofGALEX and Spitzer (~2''-6''), we assess the UV and IR properties of eachgalaxy individually. The contribution of the FUV to the measured starformation rate (SFR) ranges from 0.2% to 17.9%, with a median of 2.8%and a mean of 4.0% ± 0.4%. The specific star formation rate(SSFR) of the GOALS sample is extremely high, with a median value (3.9× 10-10 yr-1) that is comparableto the highest SSFRs seen in the Spitzer Infrared Nearby Galaxies Surveysample. We examine the position of each galaxy on the IR excess-UV slope(IRX-?) diagram as a function of galaxy properties, including IRluminosity and interaction stage. The LIRGs on average have greater IRexcesses than would be expected based on their UV colors if they obeyedthe same relations as starbursts with L IR <1011 L sun or normal late-type galaxies. The ratioof L IR to the value one would estimate from the IRX-?relation published for lower luminosity starburst galaxies ranges from0.2 to 68, with a median value of 2.7. A minimum of 19% of the total IRluminosity in the RBGS is produced in LIRGs and ultraluminous infraredgalaxies with red UV colors (?>0). Among resolved interactingsystems, 32% contain one galaxy which dominates the IR emission whilethe companion dominates the UV emission. Only 21% of the resolvedsystems contain a single galaxy which dominates both wavelengths.
| Precise Black Hole Masses from Megamaser Disks: Black Hole-Bulge Relations at Low Mass
The black hole (BH)-bulge correlations have greatly influenced the lastdecade of efforts to understand galaxy evolution. Current knowledge ofthese correlations is limited predominantly to high BH masses (MBHgsim108 M sun) that can be measuredusing direct stellar, gas, and maser kinematics. These objects, however,do not represent the demographics of more typical L < L* galaxies.This study transcends prior limitations to probe BHs that are an orderof magnitude lower in mass, using BH mass measurements derived from thedynamics of H2O megamasers in circumnuclear disks. The maserstrace the Keplerian rotation of circumnuclear molecular disks startingat radii of a few tenths of a pc from the central BH. Modeling of therotation curves, presented by Kuo et al., yields BH masses withexquisite precision. We present stellar velocity dispersion measurementsfor a sample of nine megamaser disk galaxies based on long-slitobservations using the B&C spectrograph on the Dupont telescope andthe Dual Imaging Spectrograph on the 3.5 m telescope at Apache Point. Wealso perform bulge-to-disk decomposition of a subset of five of thesegalaxies with Sloan Digital Sky Survey imaging. The maser galaxies as agroup fall below the M BH-?* relationdefined by elliptical galaxies. We show, now with very precise BH massmeasurements, that the low-scatter power-law relation between MBH and ?* seen in elliptical galaxies is notuniversal. The elliptical galaxy M BH-?*relation cannot be used to derive the BH mass function at low mass orthe zero point for active BH masses. The processes (perhaps BHself-regulation or minor merging) that operate at higher mass have noteffectively established an M BH-?* relationin this low-mass regime.
| Cold Molecular Gas in the Inner Two Kiloparsecs of NGC 4151
We present the first spatially resolved spectroscopic imagingobservations of the 12CO (1-0) line emission in the central2.5 kpc of the Seyfert 1 galaxy NGC 4151, obtained with the IRAM Plateaude Bure Interferometer (PdBI). Most of the cold molecular gas isdistributed along two curved gas lanes about 1 kpc north and south ofthe active nucleus, coincident with the circumnuclear dust ring noted byprevious authors. These CO arcs lie within the Inner Lindblad Resonanceof the large scale oval bar and have kinematics consistent with thosederived from neutral hydrogen observations of the disk and the bar. Twoadditional gas clumps are detected that show non-circularmotion—one associated with the southern gas lane and the otherlying ~600 pc north of the nucleus. Closer to the nucleus, no coldmolecular gas is detected in the central 300 pc where abundant near-IRH2 line emission arises. This suggests that the H2line emission is not a good indicator of a cold gas reservoir in NGC4151 and that the H2 is likely photo-excited by the activegalactic nucleus (AGN). The upper limit of the CO mass in the central300 pc is sufficient to support the AGN activity at its current levelfor 107 yr. The total cold molecular mass detected by PdBI is4.3 × 107 M sun. Finally, 3 mm continuumemission arising from the location of the AGN is detected with a flux ofS 3 mm ~ 14 mJy and appears to be unresolved at an angularresolution of 2farcs8 (~180 pc).Based on observations carried out with the IRAM Plateau de BureInterferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany),and IGN (Spain).
| A New Network for Higher-temperature Gas-phase Chemistry. I. A Preliminary Study of Accretion Disks in Active Galactic Nuclei
We present a new interstellar chemical gas-phase reaction network fortime-dependent kinetics that can be used for modeling high-temperaturesources up to ?800 K. This network contains an extended set ofreactions based on the Ohio State University (OSU) gas-phase chemicalnetwork. The additional reactions include processes with significantactivation energies, reverse reactions, proton exchange reactions,charge exchange reactions, and collisional dissociation. Ratecoefficients already in the OSU network are modified for H2formation on grains, ion-neutral dipole reactions, and some radiativeassociation reactions. The abundance of H2O is enhanced athigh temperature by hydrogenation of atomic O. Much of the elementaloxygen is in the form of water at T >= 300 K, leading to effectivecarbon-rich conditions, which can efficiently produce carbon-chainspecies such as C2H2. At higher temperatures, HCNand NH3 are also produced much more efficiently. We haveapplied the extended network to a simplified model of the accretion diskof an active galactic nucleus.
| Nuclear and extended spectra of NGC 1068 - II. Near-infrared stellar population synthesis
We performed stellar population synthesis on the nuclear and extendedregions of NGC 1068 by means of near-infrared spectroscopy todisentangle their spectral energy distribution components. This is thefirst time that such a technique is applied to the whole 0.8-2.4 ?mwavelength interval in this galaxy. NGC 1068 is one of the nearest andprobably the most studied Seyfert 2 galaxy, becoming an excellentlaboratory to study the interaction between black holes, the jets thatthey can produce and the medium in which they propagate. Our main resultis that traces of young stellar population are found at ~100 pc south ofthe nucleus. The contribution of a power-law continuum in the centre isabout 25 per cent, which is expected if the light is scattered from aSeyfert 1 nucleus. We find peaks in the contribution of the featurelesscontinuum about 100-150 pc from the nucleus on both sides. They might beassociated with regions where the jet encounters dense clouds. Furthersupport to this scenario is given by the peaks of hot dust distributionfound around these same regions and the H2 emission-lineprofile, leading us to propose that the peaks might be associated toregions where stars are being formed. Hot dust also has an importantcontribution to the nuclear region, reinforcing the idea of the presenceof a dense, circumnuclear torus in this galaxy. Cold dust appears mostlyin the south direction, which supports the view that the south-westemission is behind the plane of the galaxy and is extinguished verylikely by dust in the plane. Intermediate-age stellar populationcontributes significantly to the continuum, especially in the inner 200pc.
| On the anomalous silicate absorption feature of the prototypical Seyfert 2 galaxy NGC1068
ABSTRACT The first detection of the silicate absorption feature inActive Galactic Nuclei (AGNs) was made at 9.7?m for the prototypicalSeyfert 2 galaxy NGC1068 35 yr ago, indicating the presence of a largecolumn of silicate dust in the line of sight to the nucleus. It is nowwell recognized that type 2 AGNs exhibit prominent silicate absorptionbands, while the silicate bands of type 1 AGNs appear in emission. Morerecently, using the Mid-Infrared Interferometric Instrument on the VeryLarge Telescope Interferometer, Jaffe et al. for the first timespatially resolved the parsec-sized dust torus around NGC1068 and foundthat the 10?m silicate absorption feature of the innermost hotcomponent exhibits an anomalous profile differing from that of theinterstellar medium and that of common olivine-type silicate dust. Whilethey ascribed the anomalous absorption profile to gehlenite(Ca2Al2SiO7, a calcium aluminiumsilicate species), we propose a physical dust model and argue that,although the presence of gehlenite is not ruled out, the anomalousabsorption feature mainly arises from silicon carbide.
| CO Spectral Line Energy Distributions of Infrared-Luminous Galaxies and Active Galactic Nuclei
We report on new sensitive CO J = 6-5 line observations of severalluminous infrared galaxies (LIRGs; L IR(8-1000 ?m) >~1011 L sun), 36% (8/22) of them ultraluminousinfrared galaxies (ULIRGs) (L IR>1012 Lsun), and two powerful local active galactic nuclei(AGNs)—the optically luminous QSO PG 1119+120 and the powerfulradio galaxy 3C 293—using the James Clerk Maxwell Telescope onMauna Kea in Hawaii. We combine these observations with existing low-JCO data and dust emission spectral energy distributions in thefar-infrared-submillimeter from the literature to constrain theproperties of the star-forming interstellar medium (ISM) in thesesystems. We then build the first local CO spectral line energydistributions (SLEDs) for the global molecular gas reservoirs that reachup to high J-levels. These CO SLEDs are neither biased by strong lensing(which affects many of those constructed for high-redshift galaxies),nor suffer from undersampling of CO-bright regions (as most currenthigh-J CO observations of nearby extended systems do). We find: (1) asignificant influence of dust optical depths on the high-J CO lines,suppressing the J = 6-5 line emission in some of the most IR-luminousLIRGs, (2) low global CO line excitation possible even in vigorouslystar-forming systems, (3) the first case of a shock-poweredhigh-excitation CO SLED in the radio galaxy 3C 293 where a powerfuljet-ISM interaction occurs, and (4) unusually highly excitated gas inthe optically powerful QSO PG 1119+120. In Arp 220 and possibly other(U)LIRGs very faint CO J = 6-5 lines can be attributed to significantdust optical depths at short submillimeter wavelengths immersing thoselines in a strong dust continuum, and also causing the C+line luminosity deficit often observed in such extreme starbursts.Re-analysis of the CO line ratios available for submillimeter galaxiessuggests that similar dust opacities also may be present in thesehigh-redshift starbursts, with genuinely low excitation of large amountsof SF-quiescent gas being the only other possibility for their often lowCO (high-J)/(low-J) line ratios. We then present a statistical method ofseparating these two almost degenerate possibilities, and show that highdust optical depths at submillimeter wavelengths can impede thediagnostic potential of submillimeter/IR lines (e.g., starbursts versusAGNs as gas excitation agents), which is of particular importance forthe upcoming observations of the Herschel Space Observatory and the eraof ALMA.
| Misaligned Disks as Obscurers in Active Galaxies
We critically review the evidence concerning the fraction of activegalactic nuclei (AGNs) that appear as Type 2 AGNs, carefullydistinguishing strict Type 2 AGNs from both more lightly reddened Type 1AGNs, and from low excitation narrow line AGNs, which may represent adifferent mode of activity. Low-excitation AGNs occur predominantly atlow luminosities; after removing these, true Type 2 AGNs represent 58%± 5% of all AGNs, and lightly reddened Type 1 AGNs a further~15%. Radio, IR, and volume-limited samples all agree in showing nochange of Type 2 fraction with luminosity. X-ray samples do show achange with luminosity; we discuss possible reasons for thisdiscrepancy. We test a very simple picture which produces this Type 2fraction with minimal assumptions. In this picture, infall from largescales occurs in random directions, but must eventually align with theinner accretion flow, producing a severely warped disk on parsec scales.If the re-alignment is dominated by tilt, with minimal twist, a widerange of covering factors is predicted in individual objects, but withan expected mean fraction of Type 2 AGNs of exactly 50%. This "tilteddisk" picture predicts reasonable alignment of observed nuclearstructures on average, but with distinct misalignments in individualcases. Initial case studies of the few well-resolved objects show thatsuch misalignments are indeed present.
| Mid-infrared Spectroscopy of Two Lensed Star-forming Galaxies
We present low-resolution, rest-frame ~5-12 ?m Spitzer/IRS spectra oftwo lensed z ~ 2 UV-bright star-forming galaxies, SDSSJ120602.09+514229.5 and SDSS J090122.37+181432.3. Using themagnification boost from lensing, we are able to study the physicalproperties of these objects in greater detail than is possible forunlensed systems. In both targets, we detect strong polycyclic aromatichydrocarbon (PAH) emission at 6.2, 7.7, and 11.3 ?m, indicating thepresence of vigorous star formation. For J1206, we find a steeply risingcontinuum and significant [S IV] emission, suggesting that a moderatelyhard radiation field is powering continuum emission from small dustgrains. The strength of the [S IV] emission also implies a sub-solarmetallicity of ~0.5 Z sun, confirming published rest-frameoptical measurements. In J0901, the PAH lines have large rest-frameequivalent widths (>1 ?m) and the continuum rises slowly withwavelength, suggesting that any active galactic nucleus (AGN)contribution to L IR is insignificant, in contrast to theimplications of optical emission-line diagnostics. Using [O III] lineflux as a proxy for AGN strength, we estimate that the AGN in J0901provides only a small fraction of its mid-infrared continuum flux. Bycombining the detection of [Ar II] with an upper limit on [Ar III]emission, we infer a metallicity of gsim1.3 Z sun. This workhighlights the importance of combining rest-frame optical and mid-IRspectroscopy in order to understand the detailed properties ofstar-forming galaxies at high redshift.
| Search for and study of hot circumstellar dust envelopes
Long-term (1984-2008) JHKLM photometry for 254 objects is presented. Theobservations were carried out in the standard JHKLM photometric systemusing an original method and a modern IR photometer designed and builtat the Sternberg Astronomical Institute. Our program of studies includedsearches for and studies of relatively hot circumstellar dust envelopes.The most important results obtained using these observations include thefollowing. We have detected relatively hot dust envelopes in a number ofobjects for the first time, including the RCB star UV Cas, RX Cas,several classical symbiotic stars, etc. A model has been calculated forthe dust envelope of FG Sge, which formed around the star as a result ofseveral successive cycles of dust condensation beginning in Autumn 1992.Several dust-condensation episodes have been traced in the envelopes ofsymbiotic systems (CH Cyg, V1016 Cyg, HM Sge, etc.), as well as the roleof the hot component in the formation of the dust envelopes. We haveestablished from variations of the IR emission that the cool componentsin the symbiotic novae V1016 Cyg and HM Sge, and possibly CH Cyg, areMiras. The binarity of V1016 Cyg and HM Sge has also been firmlyestablished. The variability of a whole series of object has beenstudied, including the stellar components of close binary systems andseveral dozen Mira and semi-regular variables. The ellipsoidality of thecomponents in the RX Cas system (a prototype W Ser star) and the coolcomponent in the symbiotic systems CI Cyg and BF Cyg has been firmlyestablished. We have obtained the first IR light curve for the eclipsingsystem V444 Cyg (WN5+O6), and determined the wavelength dependence ofthe obtained parameters of the WN5 star. Analysis of the IR light curvesof several novae indicate the condensation of dust envelopes in thetransition periods of Cygnus 1992, Aquila 1993, and Aquila 1995. The IRlight curve of R CrB has been obtained over a long period and analyzed.IR observations of the nova-like variable V4334 Sgr have been carriedout over four years, over which the star passed through four stagesduring its motion along its post-AGB evolutionary track; the star'sbolometric flux and optical depth of its dust envelope have beenestimated, and the structure and mass of the dust layer determined. Wehave analyzed the IR variability of the symbiotic star V407 Cyg over 14years, and found its cool component to be a Mira with a period of 745days. The observed pulsations and trend are associated with theluminosity and temperature variations of the Mira, as well as theoptical depth of the dust envelope. The size of the dust grains andmass-loss rate of the Mira have been determined. We have obtained JHKLlight curves for the Seyfert galaxy NGC 4151 over 23 years. The IRbrightness of the galaxy grew from 1985 through 1996 (by ˜0.9m at 1.25 µm, ˜1 m at 1.65 µm,˜1.1 m at 2.2 µm, and ˜1.3 m at 3.5 µm), while the galaxy simultaneously reddened. The "cool"variable source in NGC 4151 was still in the active state in 1998,although its luminosity had decreased by approximately 15%-20%. If the"cool" component of the variable source in this galaxy is a dustenvelope heated by the central "hot" source, it should be optically thinto the radiation of this source: its mean optical depth is in the range0.05-0.15. Emission from dust particles heated to temperatures of600-800 K was observed in the near IR at a distance of several parsecsfrom the nucleus during the period of activity in 1995-1998; theinferred mass of emitting dust was 5-20 M ?. In1994-2003, we observed a tendency for NGC 4151 to become bluer at1.25-1.65 µm while simultaneously reddening at 2.2-3.5 µm.Beginning in Autumn 2000, the galaxy began to emerge from a minimum,which lasted from March 2000 through April 2001 in the IR; a flare ofthe galactic nucleus was observed and followed in detail in the IR inthis same period. We confirm the IR variability of the nucleus of theSeyfert galaxy NGC 1068, which can be located in various stages ofactivity. The variability of NGC 1068 is associated with a complexsource. A periodic component has been detected in the J brightnessvariations of the oxygen Mira V2108 Oph; we have shown that this star isimmersed in a fairly dense dust envelope, and have calculated amodel forthis envelope. We have calculated an (axially symmetrical) dust-envelopemodel for the carbon semi-regular variable RWLMi with a densitydistribution characteristic for the "superwind" stage. This envelopemodel is able to reproduce the observed fluxes over the entireobservable spectrum, and displays a good agreement with theobservational data. The three hot supergiants V482 Cas, QZ Sge, and HD338926 may be variable in the IR. Long-term photometry of eightplanetary nebulae in the near IR (1.25-5 µm) has enabled us tofirmly establish the IR brightness and color variability of thesenebulae on time scales from several tens of days to six-to-eight years.We have analyzed long-term JK photometry of the X-ray binary Cyg X-1(V1357 Cyg). Periodicity with a characteristic time scale of ˜11.5years is visible in the JK brightness variations of Cyg X-1 in1984-2007, possibly due to periodic variations of the temperature,radius and luminosity of the optical component of the binary with P˜11.5 yr. Fourteen-year IR light curves of five RV Tau stars (RSge, RV Tau, AC Her, V Vul, and R Sct) and the yellow supergiant andprotoplanetary-nebula candidate V1027 Cyg have been analyzed. Aspherically symmetrical dust-envelope model has been calculated forV1027 Cyg.
| Broad Balmer-Line Absorption in SDSS J172341.10+555340.5
We present the discovery of Balmer-line absorption from H? to H9in an iron low-ionizaton broad absorption line (FeLoBAL) quasar, SDSSJ172341.10+555340.5, by near-infrared spectroscopy with the CooledInfrared Spectrograph and Camera for OHS (CISCO) attached to the SubaruTelescope. The redshift of the Balmer-line absorption troughs is2.0530±0.0003, and it is blueshifted by 5370 km s-1from the Balmer emission lines. It is more than 4000 km s-1blueshifted from the previously known UV absorption lines. We detectedrelatively strong (EWrest = 20 Å)[OIII] emission lines that are similar tothose found in other broad absorption line quasars with Balmer-lineabsorption. We also derived the column density of neutral hydrogen of5.2 × 1017 cm-2 by using the curve of growthand taking account of Ly? trapping. We searched for UV absorptionlines that had the same redshift with Balmer-line absorption, and foundAliIII and FeIIIabsorption lines at z = 2.053 that correspond to previously unidentifiedabsorption lines, and the presence of other blended troughs that weredifficult to identify.
| Nuclear and extended spectra of NGC 1068 - I. Hints from near-infrared spectroscopy
We report the first simultaneous zJHK spectroscopy on the archetypicalSeyfert 2 galaxy NGC 1068 covering the wavelength region 0.9-2.4 ?m.The slit, aligned in the north-south direction and centred in theoptical nucleus, maps a region 300 pc in radius at subarcsec resolution,with a spectral resolving power of 360kms-1. Thisconfiguration allows us to study the physical properties of the nucleargas including that of the north side of the ionization cone, map thestrong excess of continuum emission in the K band and attributed to dustand study the variations, both in flux and profile, in the emissionlines. Our results show the following. (1) Mid- to low-ionizationemission lines are split into two components, whose relative strengthsvary with the position along the slit and seem to be correlated with thejet. (2) The coronal lines are single-peaked and are detected only inthe central few hundred of pc from the nucleus. (3) The absorption linesindicate the presence of intermediate age stellar population, whichmight be a significant contributor to the continuum in the near-IRspectra. (4) Through some simple photoionization models we findphotoionization as the main mechanism powering the emitting gas. (5)Calculations using stellar features point to a mass concentration insidethe 100-200 pc of about 1010Msolar.
| A study of three-dimensional kinematics of the narrow-line region of the Seyfert galaxy NGC 4151 based on integral field spectroscopy.
Not Available
| The Soft X-ray and Narrow-line Emission of Mrk 573 on Kiloparsec Scales
We present a study of the circumnuclear region of the nearby Seyfertgalaxy Mrk 573 using Chandra, XMM-Newton, and Hubble Space Telescope(HST) data. We have studied the morphology of the soft (<2 keV)X-rays comparing it with the [O III] and H? HST images. The softX-ray emission is resolved into a complex extended region. The X-raymorphology shows a biconical region extending up to 12 arcsec (4 kpc) inprojection from the nucleus. A strong correlation between the X-rays andthe highly ionized gas seen in the [O III]?5007 Å image isreported. Moreover, we have studied the line intensities detected withthe XMM-Newton Reflection Grating Spectrometer (RGS) and used them tofit the low-resolution EPIC/XMM-Newton and ACIS/Chandra spectra. TheRGS/XMM-Newton spectrum is dominated by emission lines of C VI, O VII, OVIII, Fe XVII, and Ne IX, among other highly ionized species. A good fitis obtained using these emission lines found in the RGS/XMM-Newtonspectrum as a template for Chandra spectra of the nucleus and extendedemission, coincident with the cone-like structures seen in the [OIII]/H? map. The photoionization model Cloudy provides areasonable fit for both the nuclear region and the cone-like structuresshowing that the dominant excitation mechanism is photoionization. Forthe nucleus the emission is modeled using two phases: a high ionization[log (U) = 1.23] and a low ionization [log (U) = 0.13]. For thehigh-ionization phase the transmitted and reflected components are in a1:2 ratio, whereas for the low ionization the reflected componentdominates. For the extended emission, we successfully reproduced theemission with two phases. The first phase shows a higher ionizationparameter for the northwest (log (U) = 0.9) than for the southeast cone(log (U) = 0.3). Moreover, this phase is transmission dominated for thesoutheast cone and reflection dominated for the northwest cone. Thesecond phase shows a low-ionization parameter (log (U) = -3) andis rather uniform for northwest and southeast cones and equallydistributed in reflection and transmission components. In addition, wehave also derived the optical/infrared spectral energy distribution(SED) of the nucleus from high spatial resolution images of Mrk 573. Thenuclear optical/infrared SED of the nucleus has been modeled by a clumpytorus model. The torus bolometric luminosity agrees very well with theactive galactic nucleus (AGN) luminosity inferred from the observed hardX-ray spectrum. The optical depth along the line of sight expected fromthe torus modeling indicates a high neutral hydrogen column density inagreement with the classification of the nucleus of Mrk 573 as aCompton-thick AGN.
| The HELLAS2XMM survey. XIII. Multi-component analysis of the spectral energy distribution of obscured AGN
Aims: We combine near-to-mid-IR Spitzer data with shorterwavelength observations (optical to X-rays) to get insight into theproperties of a sample of luminous, obscured active galactic nuclei(AGN). We aim at modelling their broad-band spectral energydistributions (SEDs) in order to estimate the main parameters related tothe dusty torus that is assumed to be responsible for the reprocessed IRemission. Our final goal is to estimate the intrinsic nuclearluminosities and the Eddington ratios for our luminous, obscured AGN. Methods: The sample comprises 16 obscured high-redshift (0.9? z ? 2.1), X-ray luminous quasars (L2-10 keV ~1044 erg s-1) selected from the HELLAS2XMM surveyin the 2–10 keV band. The optical-IR SEDs are described by amulti-component model that includes a stellar component to account forthe optical and near-IR emission, an AGN component that dominates in themid-IR (mainly emission from a dusty torus heated by nuclear radiation),and a starburst to reproduce the far-IR bump. A radiative transfer codeto compute the spectrum and intensity of dust reprocessed emission wasextensively tested against our multiwavelength data. While the torusparameters and the BH accretion luminosities are a direct output of theSED-fitting procedure, the BH masses were estimated indirectly by meansof the local Mbulge–MBH relation. Results: The majority (~80%) of the sources show moderate optical depth(?9.7 µm ? 3), and the derived column densitiesNH are consistent with the X-ray inferred values(1022 ? NH ? 3 × 1023cm-2) for most of the objects, confirming that the sourcesare moderately obscured Compton-thin AGN. Accretion luminosities in therange 5 × 1044 ? Lbol ? 4 ×1046 erg s-1 are inferred from the multiwavelengthfitting procedure. We compare model luminosities with those obtained byintegrating the observed SED, finding that the latter are lower by afactor of ~2 in the median. The discrepancy can be as high as an orderof magnitude for models with high optical depth (?9.7µm = 10). The ratio between the luminosities obtained by thefitting procedure and from the observed SED suggest that, at least fortype 2 AGN, observed bolometric luminosities are likely to underestimateintrinsic ones and the effect is more severe for highly obscuredsources. Bolometric corrections from the hard X-ray band are computedand have a median value of k2-10 keV ~ 20. The obscured AGNin our sample are characterized by relatively low Eddington ratios(median ?Edd ~ 0.08). On average, they are consistentwith the Eddington ratio increasing at increasing bolometric correction.
| Report on the ESO Workshop ''Central Massive Objects: The Stellar Nuclei - Black Hole Connection''
An overview of the ESO workshop on black holes and nuclear star clustersis presented. The meeting reviewed the status of our observational andtheoretical understanding of central massive objects, as well as thesearch for intermediate mass black holes in globular clusters. Therewill be no published proceedings, but presentations are available athttp://www.eso.org/sci/meetings/cmo2010/program.html.
| An Extragalactic 12CO J = 3-2 Survey with the Heinrich Hertz Telescope
We present results of a 12CO J = 3-2 survey of 125 nearbygalaxies obtained with the 10 m Heinrich Hertz Telescope, with the aimto characterize the properties of warm and dense molecular gas in alarge variety of environments. With an angular resolution of 22'',12CO 3-2 emission was detected in 114 targets. Based on 61galaxies observed with equal beam sizes the 12CO 3-2/1-0integrated line intensity ratio R 31 is found to vary from0.2 to 1.9, with an average value of 0.81. No correlations are found forR 31 to Hubble-type and far-infrared luminosity. Possibleindications for a correlation with inclination angle and the 60?m/100 ?m color temperature of the dust are not significant.Higher R 31 ratios than in "normal" galaxies, hinting atenhanced molecular excitation, may be found in galaxies hosting activegalactic nuclei. Even higher average values are determined for galaxieswith bars or starbursts, the latter being identified by the ratio ofinfrared luminosity versus isophotal area, log [(L FIR/Lsun)/(D 2 25/kpc2)] >7.25. (U)LIRGs are found to have the highest averaged R 31value. This may be a consequence of particularly vigorous star formationactivity, triggered by galaxy interaction and merger events. The nuclearCO luminosities are slightly sublinearly correlated with the global FIRluminosity in both the 12CO J = 3-2 and the 1-0 lines. Theslope of the log-log plots rises with compactness of the respectivegalaxy sub-sample, indicating a higher average density and a largerfraction of thermalized gas in distant luminous galaxies. While linearor sublinear correlations for the 12CO J = 3-2 line can beexplained, if the bulk of the observed J = 3-2 emission originates fromthe molecular gas with densities below the critical one, the case of the12CO J = 1-0 line with its small critical density remains apuzzle.
| A 158 ?m [C II] Line Survey of Galaxies at z ~ 1-2: An Indicator of Star Formation in the Early Universe
We have detected the 158 ?m [C II] line from 12 galaxies at z ~ 1-2.This is the first survey of this important star formation tracer atredshifts covering the epoch of maximum star formation in the universeand quadruples the number of reported high-z [C II] detections. The lineis very luminous, between <0.024% and 0.65% of the far-infrared (FIR)continuum luminosity of our sources, and arises from photodissociationregions on molecular cloud surfaces. An exception is PKS 0215+015, wherehalf of the [C II] emission could arise from X-ray-dominated regionsnear the central active galactic nucleus (AGN). The L [CII]/L FIR ratio in our star formation-dominated systemsis ~8 times larger than that of our AGN-dominated systems. Thereforethis ratio selects for star formation-dominated systems. Furthermore,the L [C II]/L FIR and L [C II]/L(CO(1-0)) ratios in our star-forming galaxies and nearbystarburst galaxies are the same, so that luminous star-forming galaxiesat earlier epochs (z ~ 1-2) appear to be scaled-up versions of localstarbursts entailing kiloparsec-scale starbursts. Most of the FIR and [CII] radiation from our AGN-dominated sample (excepting PKS 0215+015)also arises from kiloparsec-scale star formation, but with far-UVradiation fields ~8 times more intense than in our starformation-dominated sample. We speculate that the onset of AGN activitystimulates large-scale star formation activity within AGN-dominatedsystems. This idea is supported by the relatively strong [O III] lineemission, indicating very young stars, that was recently observed inhigh-z composite AGN/starburst systems. Our results confirm the utilityof the [C II] line, and in particular, the L [C II]/L(FIR) and L [C II]/L CO(1-0) ratios astracers of star formation in galaxies at high redshifts.
| A characterization of the NGC 4051 soft X-ray spectrum as observed by XMM-Newton
Context. Soft X-ray high resolution spectroscopy of obscured AGNs showsa complex soft X-ray spectrum dominated by emission lines of He andH-like transitions of elements from carbon to neon, as well as L-shelltransitions due to iron ions. Aims: In this paper we characterizethe XMM-Newton RGS spectrum of the Seyfert 1 galaxy NGC 4051 observedduring a low flux state and infer the physical properties of theemitting and absorbing gas in the soft X-ray regime. Methods:X-ray high-resolution spectroscopy offers a powerful diagnostic toolbecause the observed spectral features strongly depend on the physicalproperties of matter (ionization parameter U, electron densityne, hydrogen column density NH), which in turn aretightly related to the location and size of the X-ray emitting clouds.We carried out a phenomenological study to identify the atomictransitions detected in the spectra. This study suggests that thespectrum is dominated by emission from a photoionized plasma. Then weused the photoionization code Cloudy to produce synthetic models for theemission line component and the warm absorber observed during phases ofhigh intrinsic luminosity. Results: The low state spectrum cannotbe described by a single photoionization component. A multi-ionizationphase gas with an ionization parameter in the range of log U ~ 0.63-1.90and a column density log NH = 22.10-22.72 cm-2 isrequired, while the electron density ne remainsunconstrained. A warm absorber medium is required by the fit with theparameters log U ~ 0.85, log NH = 23.40 and log ne? 5. The model is consistent with an X-ray emitting region at adistance ? 5 × 10-2 pc from the central engine.
| Spectral energy distribution of hyperluminous infrared galaxies
Aims: The relationship between star formation and super-massiveblack hole growth is central to our understanding of galaxy formationand evolution. Hyperluminous infrared galaxies (HLIRG) are uniquelaboratories to investigate the connection between starburst (SB) andactive galactic nuclei (AGN), because they exhibit extremestar-formation rates, and most of them show evidence of harbouringpowerful AGN. Methods: Our previous X-ray study of a sample ofHLIRG shows that the X-ray emission of most of these sources isdominated by AGN activity. To improve our estimate of the relativecontribution of the AGN and SB emission to its total bolometric output,we have built multi-wavelength (from radio to X-rays) spectral energydistributions (SED) for these HLIRG and fitted standard empirical AGNand SB templates to these SED. Results: In broad terms, mostsources are well fitted with this method, and we found AGN and SBcontributions similar to those obtained by previous studies of HLIRG. Wehave classified the HLIRG SED into two groups, class A and class B.Class A HLIRG show a flat SED from the optical to the infrared energyrange. Three out of seven class A sources can be modelled with a pureluminosity-dependent quasar template, while the rest of them require atype 1 AGN template and a SB template. The SB component is dominant inthree out of four class A objects. Class B HLIRG show SED with aprominent and broad IR bump. These sources cannot easily be modelledwith a combination of pure AGN and pure SB, they require templates ofcomposite objects, suggesting that ?50% of their emission comes fromstellar formation processes. Conclusions: We propose that oursample is actually composed of three different populations: veryluminous quasars (class A objects with negligible SB contribution),young galaxies going through their maximal star-formation period (classA objects with significant SB emission) and the high luminosity tail ofthe ultraluminous infrared galaxies population distribution (class Bsources).
| Extended X-ray Emission in the H I Cavity of NGC 4151: Galaxy-scale Active Galactic Nucleus Feedback?
We present the Chandra discovery of soft diffuse X-ray emission in NGC4151 (L 0.5-2 keV ~ 1039 ergs–1), extending ~2 kpc from the active nucleus andfilling in the cavity of the H I material. The best fit to the X-rayspectrum requires either a kT ~ 0.25 keV thermal plasma or aphotoionized component. In the thermal scenario, hot gas heated by thenuclear outflow would be confined by the thermal pressure of the H I gasand the dynamic pressure of inflowing neutral material in the galacticdisk. In the case of photoionization, the nucleus must have experiencedan Eddington limit outburst. For both scenarios, the active galacticnucleus (AGN)-host interaction in NGC 4151 must have occurred relativelyrecently (some 104 yr ago). This very short timescale to thelast episode of high activity phase may imply such outbursts occupygsim1% of AGN lifetime.
| The dusty heart of nearby active galaxies. I. High-spatial resolution mid-IR spectro-photometry of Seyfert galaxies
In a series of papers, we aim at stepping towards characterizingphysical properties of the AGN dust torus by combining IR high-spatialresolution observations with 3D clumpy torus models. In this firstpaper, we present mid-IR imaging and 8–13 ?m low-resolutionspectroscopy of nine type 1 and ten type 2 AGN. The observations werecarried out with the VLT/VISIR mid-IR imager and spectrograph and can beconsidered the largest currently available mid-infraredspectro-photometric data set of AGN at spatial resolution ?100 pc.These data resolve scales at which the emission from the dust torusdominates the overall flux, and emission from the host galaxy (e.g.star-formation) is resolved out in most cases. The silicate absorptionfeatures are moderately deep and emission features, if seen at all, areshallow. The strongest silicate emission feature in our sample showssome notable shift of the central wavelength from the expected 9.7 ?m(based on ISM extinction curves) to ~10.5 ?m. We compare the observedmid-IR luminosities of our objects to AGN luminosity tracers (X-ray,optical and [O iii] luminosities) and find that the mid-IR radiation isemitted quite isotropically. In two cases, IC 5063 andMCG–3–34–64, we find evidence for extended dustemission in the narrow-line region. We confirm the correlation betweenobserved silicate feature strength and Hydrogen column density, whichwas recently found in Spitzer data at lower spatial resolution. In afurther step, our 3D clumpy torus model has been used to interpret thedata. We show that the strength of the silicate feature and the mid-IRspectral index ? can be used to get reasonable constraints on theradial dust distribution of the torus and the average number of cloudsN0 along an equatorial line-of-sight in clumpy torus models.The mid-IR spectral index ? is almost exclusively determined bythe radial dust distribution power-law index a, while the silicatefeature depth mostly depends on N0 and the torus inclination.A comparison of model predictions to our type 1 and type 2 AGN revealsthat average parameters of a = –1.0±0.5 and N0 =5–8 are typically seen in the presented sample, which means thatthe radial dust distribution is rather shallow. As a proof-of-concept ofthis method, we compared the model parameters derived from ? andthe silicate feature strength to more detailed studies of full IR SEDsand interferometry and found that the constraints on a and N0are consistent. Finally, we may have found evidence that the radialstructure of the torus changes from low to high AGN luminosities towardssteeper dust distributions, and we discuss implications for the IRsize-luminosity relation.Based on ESO observing programs 078.B-0303, 080.B-0240, 280.B-5068,082.B-0299, and 083.B-0239.
| Gas dynamics of the central few parsec region of NGC 1068 fuelled by the evolving nuclear star cluster
ABSTRACT Recently, high-resolution observations with the help of thenear-infrared adaptive optics integral field spectrograph Spectrographfor INtegral Field Observations in the Near Infrared (SINFONI) at theVery Large Telescope proved the existence of massive and young nuclearstar clusters in the centres of a sample of Seyfert galaxies. With thehelp of three-dimensional high-resolution hydrodynamical simulationswith the PLUTO code, we follow the evolution of such clusters,especially focusing on stellar mass loss feeding gas into the ambientinterstellar medium and driving turbulence. This leads to a verticallywide distributed clumpy or filamentary inflow of gas on large scales(tens of parsec), whereas a turbulent and very dense disc builds up onthe parsec scale. In order to capture the relevant physics in the innerregion, we treat this disc separately by viscously evolving the radialsurface density distribution. This enables us to link the tens ofparsec-scale region (accessible via SINFONI observations) to the(sub-)parsec-scale region (observable with the mid-infraredinterferometer instrument and via water maser emission). Thereby, thisprocedure provides us with an ideal testbed for data comparison. In thiswork, we concentrate on the effects of a parametrized turbulentviscosity to generate angular momentum and mass transfer in the disc andadditionally take star formation into account. Most of the inputparameters are constrained by available observations of the nearbySeyfert 2 galaxy NGC 1068, and we discuss parameter studies for the freeparameters. At the current age of its nuclear starburst of 250Myr, oursimulations yield disc sizes of the order of 0.8-0.9pc, gas masses of106Msolar and mass transfer rates of0.025Msolaryr-1 through the inner rim of the disc.This shows that our large-scale torus model is able to approximatelyaccount for the disc size as inferred from interferometric observationsin the mid-infrared and compares well to the extent and mass of arotating disc structure as inferred from water maser observations.Several other observational constraints are discussed as well.
| A Chandra Perspective on Galaxy-wide X-ray Binary Emission and its Correlation with Star Formation Rate and Stellar Mass: New Results from Luminous Infrared Galaxies
We present new Chandra observations that complete a sample of seventeen(17) luminous infrared galaxies (LIRGs) with D < 60 Mpc and lowGalactic column densities of N H <~ 5 ×1020 cm-2. The LIRGs in our sample havetotal infrared (8-1000 ?m) luminosities in the range of LIR? (1-8) × 1011 L sun. Thehigh-resolution imaging and X-ray spectral information from our Chandraobservations allow us to measure separately X-ray contributions fromactive galactic nuclei and normal galaxy processes (e.g., X-ray binariesand hot gas). We utilized total infrared plus UV luminosities toestimate star formation rates (SFRs) and K-band luminosities and opticalcolors to estimate stellar masses (M sstarf) for the sample.Under the assumption that the galaxy-wide 2-10 keV luminosity (Lgal HX) traces the combined emission fromhigh-mass X-ray binaries (HMXBs) and low-mass X-ray binaries, and thatthe power output from these components is linearly correlated with SFRand M sstarf, respectively, we constrain the relation Lgal HX = ?M sstarf + ?SFR.To achieve this, we construct a Chandra-based data set composed of ournew LIRG sample combined with additional samples of less activelystar-forming normal galaxies and more powerful LIRGs and ultraluminousinfrared galaxies (ULIRGs) from the literature. Using these data, wemeasure best-fit values of ? = (9.05 ± 0.37) ×1028 erg s-1 M -1sun and ? = (1.62 ± 0.22) × 1039erg s-1 (M sunyr-1)-1. This scaling provides a morephysically meaningful estimate of L gal HX, with?0.1-0.2 dex less scatter, than a direct linear scaling with SFR. Ourresults suggest that HMXBs dominate the galaxy-wide X-ray emission forgalaxies with SFR/M sstarf gsim5.9 ×10-11 yr-1, a factor of ?2.9 timeslower than previous estimates. We find that several of the most powerfulLIRGs and ULIRGs, with SFR/M sstarf >~10-9 yr-1, appear to be X-rayunderluminous with respect to our best-fit relation. We argue that thesegalaxies are likely to contain X-ray binaries residing in compactstar-forming regions that are buried under thick galactic columns largeenough to attenuate emission in the 2-10 keV band (N H >~1023 cm-2).
| The Radio Continuum, Far-Infrared Emission, and Dense Molecular Gas in Galaxies
A tight linear correlation is established between the HCN lineluminosity and the radio continuum (RC) luminosity for a sample of 65galaxies (from Gao & Solomon's HCN survey), including normal spiralgalaxies and luminous and ultraluminous infrared galaxies(LIRGs/ULIRGs). After analyzing the various correlations among theglobal far-infrared (FIR), RC, CO, and HCN luminosities and theirvarious ratios, we conclude that the FIR-RC and FIR-HCN correlationsappear to be linear and are the tightest among all correlations. Thecombination of these two correlations could result in the tight RC-HCNcorrelation we observed. Meanwhile, the nonlinear RC-CO correlationshows slightly larger scatter as compared with the RC-HCN correlation,and there is no correlation between ratios of either RC/HCN-CO/HCN orRC/FIR-CO/FIR. In comparison, a meaningful correlation is still observedbetween ratios of RC/CO-HCN/CO. Nevertheless, the correlation betweenRC/FIR and HCN/FIR also disappears, reflecting again the two tightestFIR-RC and FIR-HCN correlations as well as suggesting that FIR seems tobe the bridge that connects HCN with RC. Interestingly, despite obviousHCN-RC and RC-CO correlations, multi-parameter fits hint that while bothRC and HCN contribute significantly (with no contribution from CO) toFIR, yet RC is primarily determined from FIR with a very smallcontribution from CO and essentially no contribution from HCN. Theseanalyses independently confirm previous conclusions that it is practicalto use RC luminosity instead of FIR luminosity, at least globally, as anindicator of star formation rate in galaxies including LIRGs/ULIRGs, andHCN is a much better tracer of star-forming molecular gas and correlateswith FIR much better than CO.
| Molecular gas chemistry in AGN. II. High-resolution imaging of SiO emission in NGC 1068: shocks or XDR?
Context. This paper is part of a multi-species survey of line emissionfrom the molecular gas in the circum-nuclear disk (CND) of the Seyfert 2galaxy NGC 1068. Unlike in other active galaxies, the intenselystar-forming regions in NGC 1068 and the CND can be resolved withcurrent instrumentation. This makes this galaxy an optimal test-bed toprobe the effects of AGN on the molecular medium at ~100 pc scales. Aims: Single-dish observations have provided evidence that theabundance of silicon monoxide (SiO) in the CND of NGC 1068 is enhancedby 3-4 orders of magnitude with respect to the values typically measuredin quiescent molecular gas in the Galaxy. We aim at unveiling themechanism(s) underlying the SiO enhancement. Methods: We haveimaged the emission of the SiO(2-1) (86.8 GHz) and CN(2-1) (226.8 GHz)lines in NGC 1068 at ~150 pc and 60 pc spatial resolution with the IRAMPlateau de Bure interferometer (PdBI). We have also obtainedcomplementary IRAM 30 m observations of HNCO and methanol(CH3OH) lines. These species are known as tracers of shocksin the Galaxy. Results: SiO is detected in a disk of ~400 pc sizearound the AGN. SiO abundances in the CND of ~(1-5) ×10-9 are about 1-2 orders of magnitude above those measuredin the starburst ring. The overall abundance of CN in the CND is high:~(0.2-1) × 10-7. The abundances of SiO and CN areenhanced at the extreme velocities of gas associated with non-circularmotions close to the AGN (r < 70 pc). On average, HNCO/SiO andCH3OH/SiO line ratios in the CND are similar to thosemeasured in prototypical shocked regions in our Galaxy. Yet the strengthand abundance of CN in NGC 1068 can be explained neither by shocks norby photon-dominated region (PDR) chemistry. Abundances measured for CNand SiO and the correlation of CN/CO and SiO/CO ratios with hard X-rayirradiation suggest that the CND of NGC 1068 has become a giantX-ray-dominated region (XDR). Conclusions: The extreme propertiesof molecular gas in the circum-nuclear molecular disk of NGC 1068 resultfrom the interplay between different processes directly linked tonuclear activity. The results presented here highlight in particular thefootprint of shocks and X-ray irradiation on the properties of moleculargas in this Seyfert. Whereas XDR chemistry offers a simple explanationfor CN and SiO in NGC 1068, the relevance of shocks deserves furtherscrutiny. The inclusion of dust grain chemistry would help solve thecontroversy regarding the abundances of other molecular species, likeHCN, which are under-predicted by XDR models.Based on observations carried out with the IRAM Plateau de BureInterferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany)and IGN (Spain).
| The AGN, Star-forming, and Morphological Properties of Luminous IR-bright/optically-faint Galaxies
We present the active galactic nucleus (AGN), star-forming, andmorphological properties of a sample of 13 MIR-luminous (f 24>~ 700 ?Jy) IR-bright/optically-faint galaxies (IRBGs, f24/f R >~ 1000). While these z ~ 2 sources weredrawn from deep Chandra fields with >200 ks X-ray coverage, onlyseven are formally detected in the X-ray and four lack X-ray emission ateven the 2? level. Spitzer InfraRed Spectrograph (IRS) spectra,however, confirm that all of the sources are AGN-dominated in themid-IR, although half have detectable polycyclic aromatic hydrocarbon(PAH) emission responsible for ~25% of their mid-infrared flux density.When combined with other samples, this indicates that at least 30%-40%of luminous IRBGs have star formation rates in the ultraluminousinfrared galaxy (ULIRG) range (~100-2000 M sunyr–1). X-ray hardness ratios and MIR to X-rayluminosity ratios indicate that all members of the sample containheavily X-ray obscured AGNs, 80% of which are candidates to be Comptonthick. Furthermore, the mean X-ray luminosity of the sample, log L2-10 keV (erg s–1) ~44.6, indicates thatthese IRBGs are Type 2 QSOs, at least from the X-ray perspective. Whilethose sources most heavily obscured in the X-ray are also those mostlikely to display strong silicate absorption in the mid-IR, silicateabsorption does not always accompany X-ray obscuration. Finally, ~70% ofthe IRBGs are merger candidates, a rate consistent with that of sub-mmgalaxies (SMGs), although SMGs appear to be physically larger thanIRBGs. These characteristics are consistent with the proposal that theseobjects represent a later, AGN-dominated, and more relaxed evolutionarystage following soon after the star-formation-dominated one representedby the SMGs.
| Evolution of the ISM in luminous infrared galaxies
Aims: Molecules that trace the high-density regions of theinterstellar medium may be used to evaluate the changing physical andchemical environment during the ongoing nuclear activity in(ultra-)luminous infrared galaxies (ULIRGs). Methods: Thechanging ratios of the HCN (1-0), HNC (1-0), HCO+ (1-0), CN(1-0) and CN (2-1), and CS (3-2) transitions were compared with the HCN(1-0)/CO (1-0) ratio, which is proposed to represent the progressiontime scale of the starburst. These diagnostic diagrams were interpretedusing the results of theoretical modeling with a large physical andchemical network to describe the state of the nuclear ISM in theevolving galaxies. Results: Systematic changes are seen in theline ratios as the sources evolve from early stage for the nuclearstarburst (ULIRGs) to later stages. These changes result from changingenvironmental conditions and particularly from the lowering of theaverage density of the medium. A temperature rise due to mechanicalheating of the medium by feedback explains the lowering of the ratios atlater evolutionary stages. Infrared pumping may affect the CN and HNCline ratios during early evolutionary stages. Conclusions:Molecular transitions display a behavior that relates to changes of theenvironment during an evolving nuclear starburst. Molecular propertiesmay be used to designate the evolutionary stage of the nuclearstarburst. The HCN(1-0)/CO(1-0) and HCO+(1-0)/HCN(1-0) ratiosserve as indicators of the time evolution of the outburst.
| Mid-infrared Spectroscopy of Candidate Active Galactic Nuclei-dominated Submillimeter Galaxies
Spitzer spectroscopy has revealed that sime80% of submm galaxies (SMGs)are starburst (SB)-dominated in the mid-infrared. Here we focus on theremaining sime20% that show signs of harboring powerful active galacticnuclei (AGNs). We have obtained Spitzer-InfraRed Spectrographspectroscopy of a sample of eight SMGs that are candidates for harboringpowerful AGNs on the basis of IRAC color selection (S 8?m/S 4.5 ?m>2, i.e., likely power-lawmid-infrared spectral energy distributions). SMGs with an AGN dominating(gsim50%) their mid-infrared emission could represent the "missing link"sources in an evolutionary sequence involving a major merger. First ofall, we detect polycyclic aromatic hydrocarbon (PAH) features in all ofthe SMGs, indicating redshifts from 2.5 to 3.4, demonstrating the powerof the mid-infrared to determine redshifts for these optically faintdusty galaxies. Second, we see signs of both star formation (from thePAH features) and AGN activity (from continuum emission) in our sample:62% of the sample are AGN-dominated in the mid-infrared with a medianAGN content of 56%, compared with <30% on average for typical SMGs,revealing that our IRAC color selection has successfully singled outsources with proportionately more AGN emission than typical SB-dominatedSMGs. However, we find that only about 10% of these AGNs dominate thebolometric emission of the SMG when the results are extrapolated tolonger infrared wavelengths, implying that AGNs are not a significantpower source to the SMG population overall, even when there is evidencein the mid-infrared for substantial AGN activity. When existing samplesof mid-infrared AGN-dominated SMGs are considered, we find that S 8?m/S 4.5 ?m>1.65 works well at selectingmid-infrared energetically dominant AGNs in SMGs, implying a duty cycleof ~15% if all SMGs go through a subsequent mid-infrared AGN-dominatedphase in the proposed evolutionary sequence.
| X-ray imaging of the ionisation cones in NGC 5252
Context. The physical conditions of the gas forming the narrow-lineregions (NLR) in active galactic nuclei (AGN) have been extensivelystudied in the optical band. Recently detailed X-ray studies have shownhow the emission in the 0.1–2 keV band detected in Seyfert 2galaxies is associated to gas lying close to or associated with the NLR. Aims: We take advantage of the spectacular extension (~15”)of the NLR in the type II Seyfert galaxy NGC 5252 and of thecomplementary characteristics of XMM-Newton and Chandra to investigatethe physical conditions of the gas in this galaxy. Methods: TheX-ray data from XMM-Newton are used to define the spectral properties ofthe ionising nuclear source. The Chandra data are used to trace thespatial characteristics of the soft X-ray emission. This information isthen compared to the optical HST characteristics of the NLR in NGC 5252. Results: The X-ray spectrum of the nucleus of NGC 5252 isintrinsically flat (?~1.4–1.5) and absorbed by neutral gaswith a column density NH~1022 cm-2.Below ~1 keV a soft excess is detected. The high-resolution spectrumobtained with the XMM-Newton RGS shows emission lines in the0.2–1.5 keV range which strongly indicate that the soft X-raycomponent is essentially due to ionised gas. Moreover, the soft X-rayemission is spatially resolved around the nucleus and well overlaps theimages obtained in narrow optical bands centred around the [Oiii]emission line at 5007 Å. The [Oiii]/soft-X flux ratios along theionisation cones are basically constant. This indicates that theelectron density does not significantly deviate from the r-2law (constant ionisation parameter) moving outward from the nucleus. Conclusions: This result combined with previous optical studiessuggests two plausible but different scenarios in the reconstruction ofthe last ~30 000 years of history of the central AGN. The most promisingone is that the source is indeed a “quasar relic” with asteady and inefficient energy release from the accretion of matter ontothe central super-massive black-hole. This scenario is suggested also bythe flat nuclear X-ray spectrum that evokes an advection dominatedaccretion flow (ADAF) like emission mechanism.
| The LABOCA Survey of the Extended Chandra Deep Field South: Two Modes of Star Formation in Active Galactic Nucleus Hosts?
We study the co-existence of star formation and active galactic nucleus(AGN) activity in Chandra X-ray-selected AGN by analyzing stacked 870?m submillimeter emission from a deep and wide map of the ExtendedChandra Deep Field South (ECDFS), obtained with the LABOCA instrument atthe APEX telescope. The total X-ray sample of 895 sources with medianredshift z ~ 1 drawn from the combined (E)CDFS X-ray catalogs isdetected at >11? significance at a mean submillimeter flux of0.49 ± 0.04 mJy, corresponding to a typical star formation rate(SFR) around 30 M sun yr-1 for a T = 35 K,? = 1.5 graybody far-infrared spectral energy distribution. Thegood signal-to-noise ratio permits stacking analyses for majorsubgroups, splitting the sample by redshift, intrinsic luminosity, andAGN obscuration properties. We observe a trend of SFR increasing withredshift. An increase of SFR with AGN luminosity is indicated at thehighest L 2-10 keV >~ 1044 ergs-1 luminosities only. Increasing trends with X-rayobscuration as expected in some AGN evolutionary scenarios are notobserved for the bulk of the X-ray AGN sample but may be present for thehighest intrinsic luminosity objects with L 2-10 keV >~1044 erg s-1. This behavior suggests atransition between two modes in the co-existence of AGN activity andstar formation. For the bulk of the sample, the X-ray luminosity andobscuration of the AGN are not intimately linked to the global SFR oftheir hosts. The hosts are likely massive and forming stars secularly,at rates similar to the pervasive star formation seen in massivegalaxies without an AGN at similar redshifts. In these systems, starformation is not linked to a specific state of the AGN and the period ofmoderately luminous AGN activity may not highlight a major evolutionarytransition of the galaxy. The change indicated toward more intense starformation, and a more pronounced increase in SFRs between unobscured andobscured AGN reported in the literature at highest (L 2-10keV >~ 1044 erg s-1) luminositiessuggests that these luminous AGNs follow an evolutionary path on whichobscured AGN activity and intense star formation are linked, possiblyvia merging. Comparison to local hard X-ray-selected AGN supports thisinterpretation. SFRs in the hosts of moderate luminosity AGN at z ~ 1are an order of magnitude higher than at z ~ 0, following the increasein the non-AGN massive galaxy population. At high AGN luminosities,hosts on the evolutionary link/merger path emerge from this secularlevel of star formation.
| On the interpretation of the apparent existence of a preferred magnetic polarity in extragalactic jet sources
Contopoulos et al. recently argued that there is observational evidencefor a preferred sense of the Faraday rotation-measure gradients acrossjets from active galactic nuclei (AGNs). Such behaviour could arise ifthere were a deterministic relationship between the polarity of thepoloidal magnetic field that threads the outflow and the sense ofrotation of the outflow's source. Based on this interpretation,Countopoulos et al. suggested that their finding supports a model forthe origin of cosmic magnetic fields in a Poynting-Robertson processoperating in AGN accretion discs. Here I point out that an alternativeexplanation of such a relationship could be that the Hall current playsa key role in the magnetohydrodynamics of the underlying disc. In thispicture, the measured Faraday rotation is dominated by the contributionof a centrifugally driven wind that is launched from the weakly ionizedouter region of the disc. Additional observations are, however, neededto verify the claimed behaviour.
| Adaptive optics near infrared integral field spectroscopy of NGC 2992
Aims: NGC 2992 is an intermediate Seyfert 1 galaxy showingoutflows on kilo parsec scales which might be due either to AGN orstarburst activity. We therefore aim at investigating its central regionfor a putative starburst in the past and its connection to the AGN andthe outflows. Methods: Observations were performed with theadaptive optics near infrared integral field spectrograph SINFONI on theVLT, complemented by longslit observations with ISAAC on the VLT, aswell as N- and Q-band data from the Spitzer archive. The spatial andspectral resolutions of the SINFONI data are 50 pc and 83 kms-1, respectively. The field of view of 3 arcsec × 3arcsec corresponds to 450 pc × 450 pc. Br? equivalent widthand line fluxes from PAHs were compared to stellar population models toconstrain the age of the putative recent star formation. A simplegeometric model of two mutually inclined disks and an additional cone todescribe an outflow was developed to explain the observed complexvelocity field in H2 1-0S(1). Results: Themorphologies of the Br? and the stellar continuum are differentsuggesting that at least part of the Br? emission comes from theAGN. This is confirmed by PAH emission lines at 6.2 ?m and 11.2 ?mand the strength of the silicon absorption feature at 9.7 ?m, whichpoint to dominant AGN activity with a relatively minor starburstcontribution. We find a starburst age of 40-50 Myr from Br? linediagnostics and the radio continuum; ongoing star formation can beexcluded. Both the energetics and the timescales indicate that theoutflows are driven by the AGN rather than the starburst. The complexvelocity field observed in H2 1-0S(1) in the central 450 pccan be explained by the superposition of the galaxy rotation and anoutflow.Based on observations collected at the European Southern Observatory,Chile (074.B-9012).
| Herschel-PACS spectroscopy of IR-bright galaxies at high redshift
We present Herschel-PACS observations of rest-frame mid-infrared andfar-infrared spectral line emissions from two lensed, ultra-luminousinfrared galaxies at high redshift: MIPS J142824.0+352619 (MIPS J1428),a starburst-dominated system at z = 1.3, and IRAS F10214+4724 (F10214),a source at z = 2.3 hosting both star-formation and a luminous AGN. Wehave detected [O I]63?m and [O III]52?m in MIPS J1428, andtentatively [O III]52?m in F10214. Together with the recent ZEUS-CSO[C II]158?m detection in MIPS J1428 we can for the first time combine[O I], [C II] and far-IR (FIR) continuum measurements for PDR modelingof an ultra-luminous (LIR?1012~L_?) starforming galaxy at the peak epoch of cosmic star formation. We find thatMIPS J1428, contrary to average local ULIRGs, does not show a deficit in[O I] relative to FIR. The combination of far-UV flux G0 andgas density n (derived from the PDR models), as well as the starformation efficiency (derived from CO and FIR) is similar to normal orstarburst galaxies, despite the high infrared luminosity of this system.In contrast, F10214 has stringent upper limits on [O IV] and [S III],and an [O III]/FIR ratio at least an order of magnitude lower than localstarbursts or AGN, similar to local ULIRGs.Herschel is an ESA space observatory with science instruments providedby European-led Principal Investigator consortia and with importantparticipation from NASA.
| Probing high-redshift quasars with ALMA. I. Expected observables and potential number of sources
Aims: We explore how ALMA observations can probe high-redshiftgalaxies in unprecedented detail. We discuss the main observables thatare excited by the large-scale starburst, and formulate expectations forthe chemistry and the fluxes in the center of active galaxies, in whichchemistry may be driven by the absorption of X-rays. We estimate theexpected number of sources at high redshift in an ALMA deep field. As aspecific example for the complex interpretation of sub-mm lineobservations, we analyze the recently detected z = 6.42 quasar, forwhich a number of different line fluxes is already available. We notethat our diagnostics may also be valuable for future observations in thelocal universe with space-borne instruments like on SPICA or FIRI. Methods: To estimate the observables from the starburst, we checkwhich emission from the starburst ring of the nearby Seyfert 2 galaxyNGC 1068 falls into the ALMA bands if the galaxy were placed at z = 8.We estimate the sizes of the central X-ray dominated region based on asemi-analytic model, and employ a detailed 1D approach for the chemistryin X-ray irradiated molecular clouds to evaluate the chemistry and theexpected line emission under these conditions. We make use ofpre-existing chemistry calculations in X-ray dominated regions to showthe dependence of different line fluxes on X-ray luminosity, clouddensity and cloud column density. We use theoretical models for thehigh-z black hole population and the local SMBH density to estimate thenumber of sources at higher redshift. Results: We show that anumber of different fine-structure lines may be used to probe thestarburst component of high-redshift quasars in considerable detail,providing specific information on the structure of these galaxies byseveral independent means. We show that the size of the central X-raydominated region is of the order of a few hundred parsec, and we providedetailed predictions for the expected fluxes in CO, [CII] and [OI].While the latter fine-structure lines quickly become optically thick anddepend mostly on the strength of the X-ray source, the rotational COlines have a non-trivial dependence on these parameters. We compare ourmodels to XDRs observed in NGC 1068 and APM 08279 and find that theobserved emission can indeed be explained with these models. Dependingon the amount of X-ray flux, the CO line intensities may risecontinuously up to the (17-16) transition. A measurement of such high-Jlines allows one to distinguish observationally between XDRs and PDRs.For the recently observed z = 6.42 quasar, we show that the collectedfluxes cannot be interpreted in terms of a single gas component. We findindications for the presence of a dense warm component in active starforming regions and a low-density component in more quiescent areas.Near z = 6, an ALMA deep field may find roughly one source perarcmin2. At higher redshift, one likely has to rely on othersurveys like JWST to find appropriate sources.
| Infrared Spectral Energy Distributions of Seyfert Galaxies: Spitzer Space Telescope Observations of the 12 μm Sample of Active Galaxies
The mid-infrared spectral energy distributions (SEDs) of 83 activegalaxies, mostly Seyfert galaxies, selected from the extended 12 μmsample are presented. The data were collected using all threeinstruments, Infrared Array Camera (IRAC), Infrared Spectrograph (IRS),and Multiband Imaging Photometer for Spitzer (MIPS), aboard the SpitzerSpace Telescope. The IRS data were obtained in spectral mapping mode,and the photometric data from IRAC and IRS were extracted from matched,20'' diameter circular apertures. The MIPS data were obtained in SEDmode, providing very low-resolution spectroscopy (R ~ 20) between ~55and 90 μm in a larger, 20'' × 30'' synthetic aperture. Wefurther present the data from a spectral decomposition of the SEDs,including equivalent widths and fluxes of key emission lines; silicate10 μm and 18 μm emission and absorption strengths; IRACmagnitudes; and mid-far-infrared spectral indices. Finally, we examinethe SEDs averaged within optical classifications of activity. We findthat the infrared SEDs of Seyfert 1s and Seyfert 2s with hidden broadline regions (HBLRs, as revealed by spectropolarimetry or othertechnique) are qualitatively similar, except that Seyfert 1s showsilicate emission and HBLR Seyfert 2s show silicate absorption. Theinfrared SEDs of other classes within the 12 μm sample, includingSeyfert 1.8-1.9, non-HBLR Seyfert 2 (not yet shown to hide a type 1nucleus), LINER, and H II galaxies, appear to be dominated by starformation, as evidenced by blue IRAC colors, strong polycyclic aromatichydrocarbon emission, and strong far-infrared continuum emission,measured relative to mid-infrared continuum emission.
| The X-ray to [Ne V]3426 flux ratio: discovering heavily obscured AGN in the distant Universe
We investigate the possibility of using the ratio between the 2-10keV flux and the [Ne V]3426 emission line flux (X/NeV) as a diagnosticdiagram to discover heavily obscured, possibly Compton-thick activegalactic nuclei (AGN) in the distant Universe. While it is on averageabout one order of magnitude fainter than the more commonly used [OIII]5007 emission line, the [Ne V]3426 line can be observed with opticalspectroscopy up to z~1.5, whereas the [O III]5007 line is redshifted outof the optical bands already at z~0.8. First, we calibrated a relationbetween X/NeV and the cold absorbing column density NH usinga sample of 74 bright, nearby Seyferts with both X-ray and [Ne V] dataavailable in the literature and for which the column density isdetermined unambiguously. Similar to what is found for the X-ray to [OIII]5007 flux ratio (X/OIII), we found that the X/NeV ratio decreasestowards high column densities, as expected if [Ne V]3426 emission is agood tracer of the AGN intrinsic power. Essentially all local Seyfertswith X/NeV values below 15 are found to be Compton-thick objects. AtX/NeV values below 100, the percentage of Compton-thick nuclei decreasesto ~50%, but ~80% of the considered sample is still absorbed withNH > 1023 cm-2. Second, we appliedthis diagnostic diagram to different samples of distant obscured andunobscured QSOs in the Sloan Digital Sky Survey (SDSS). SDSS blue,unobscured, type-1 QSOs in the redshift range z = [0.1-1.5] indeedshow X/NeV values typical of unobscured Seyfert 1s in the localUniverse. Conversely, SDSS type-2 QSOs at z~0.5 classified either asCompton-thick or Compton-thin on the basis of their X/OIII ratio, wouldhave mostly been classified in the same way based on the X/NeV ratio. Weapplied the X/NeV diagnostic diagram to 9 SDSS obscured QSOs in theredshift range z = [0.85-1.31], selected by means of theirprominent [Ne V]3426 line (rest EW > 4 Å) and observed withChandra ACIS-S for 10ks each (8 of them as part of our proprietaryprogram). Based on the X/NeV ratio, complemented by X-ray spectralanalysis, 2 objects appear good Compton-thick QSO candidates, 4 objectsappear as Compton-thin QSOs, while 3 have an ambiguous classification.When excluding broad-lined QSOs with a red continuum from the sample andthus considering only genuine narrow-line objects, the efficiency inselecting Compton-thick QSOs through the [Ne V] line is about 50% (withlarge errors, though), more similar to what is achieved with [O III]selection. We discuss the possibility of applying the X/NeV diagnosticto deep X-ray surveys to search for Compton-thick Seyferts at z~1, i.e.,those objects that are thought to be responsible for the“missing” X-ray background. Finally, we compared the opticalspectral properties of [Ne V]-selected QSOs with those of other SDSSpopulations of obscured and unobscured QSOs. By restricting the analysisto objects in the same redshift (and luminosity) range z =[0.4-1.5], we found evidence that, at any given [Ne V] luminosity,increasing obscuration is accompanied by increasing [O II]3727 emission.This correlation is interpreted as evidence of enhanced star formationin obscured QSOs, which is consistent with current popular scenarios ofBH-galaxy coevolution.
| Herschel unveils a puzzling uniformity of distant dusty galaxies
The Herschel Space Observatory enables us to accurately measure thebolometric output of starburst galaxies and active galactic nuclei (AGN)by directly sampling the peak of their far-infrared (IR) emission. Herewe examine whether the spectral energy distribution (SED) and dusttemperature of galaxies have strongly evolved over the last 80% of theage of the Universe. We discuss possible consequences for thedetermination of star-formation rates (SFR) and any evidence for a majorchange in their star-formation properties. We use Herschel deepextragalactic surveys from 100 to 500 ?m to compute total IRluminosities in galaxies down to the faintest levels, using PACS andSPIRE in the GOODS-North field (PEP and HerMES key programs). Anextension to fainter luminosities is done by stacking images on 24 ?mprior positions. We show that measurements in the SPIRE bands can beused below the statistical confusion limit if information at higherspatial resolution is used, e.g. at 24 ?m, to identify“isolated” galaxies whose flux is not boosted by brightneighbors. Below z 1.5, mid-IR extrapolations are correct forstar-forming galaxies with a dispersion of only 40% (0.15 dex),therefore similar to z 0 galaxies, over three decades in luminositybelow the regime of ultra-luminous IR galaxies (ULIRGs, LIR? 1012 Lsun). This narrow distribution ispuzzling when considering the range of physical processes that couldhave affected the SED of these galaxies. Extrapolations from only one ofthe 160 ?m, 250 ?m or 350 ?m bands alone tend to overestimatethe total IR luminosity. This may be explained by the lack of far-IRconstraints around and above 150 ?m (rest-frame) before Herschel onthose templates. We also note that the dust temperature of luminous IRgalaxies (LIRGs, LIR ? 1011 Lsun)around z 1 is mildly colder by 10-15% than their local analogs and upto 20% for ULIRGs at z 1.6 (using a single modified blackbody-fit tothe peak far-IR emission with an emissivity index of ? = 1.5).Above z = 1.5, distant galaxies are found to exhibit a substantiallylarger mid- over far-IR ratio, which could either result from strongerbroad emission lines or warm dust continuum heated by a hidden AGN. Twothirds of the AGNs identified in the field with a measured redshiftexhibit the same behavior as purely star-forming galaxies. Hence a largefraction of AGNs harbor coeval star formation at very high SFR and inconditions similar to purely star-forming galaxies.Herschel is an ESA space observatory with science instruments providedby European-led Principal Investigator consortia and with importantparticipation from NASA.
| Three-Dimensional Integral Field Observations of 10 Galactic Winds. I. Extended Phase (gsim10 Myr) of Mass/Energy Injection Before the Wind Blows
In recent years, we have come to recognize the widespread importance oflarge-scale winds in the life cycle of galaxies. The onset and evolutionof a galactic wind is a highly complex process which must be understoodif we are to understand how energy and metals are recycled throughoutthe galaxy and beyond. Here we present three-dimensional spectroscopicobservations of a sample of 10 nearby galaxies with the AAOmega-SPIRALintegral-field spectrograph on the 3.9 m Anglo-Australian Telescope, thelargest survey of its kind to date. The double-beam spectrographprovides spatial maps in a range of spectral diagnostics: [O III]5007,Hβ, Mg b, Na D, [O I]6300, Hα, [N II]6583, [S II]6717, 6731.We demonstrate that these flows can often separate into highly orderedstructures through the use of ionization diagnostics and kinematics. Allof the objects in our survey show extensive wind-driven filamentationalong the minor axis, in addition to large-scale disk rotation. Oursample can be divided into either starburst galaxies or active galacticnuclei (AGNs), although some objects appear to be a combination ofthese. The total ionizing photon budget available to both classes ofgalaxies is sufficient to ionize all of the wind-blown filamentation outto large radius. We find, however, that while AGN photoionization alwaysdominates in the wind filaments, this is not the case in starburstgalaxies where shock ionization dominates. This clearly indicates thatafter the onset of star formation, there is a substantial delay (gsim10Myr) before a starburst wind develops. We show why this behavior isexpected by deriving "ionization" and dynamical timescales for both AGNsand starbursts. We establish a sequence of events that lead to the onsetof a galactic wind. The clear signature provided by the ionizationtimescale is arguably the strongest evidence yet that the starburstphenomenon is an impulsive event. A well-defined ionization timescale isnot expected in galaxies with a protracted history of circumnuclear starformation. Our three-dimensional data provide important templates forcomparisons with high-redshift galaxies.
| XMM-Newton observations of the hot spot galaxy NGC 2903
We report on the first deeper X-ray broad-band observation of the hotspot galaxy NGC 2903 obtained with XMM-Newton. X-ray imaging and spectraof the spiral barred galaxy NGC 2903 were obtained from XMM-Newtonarchival data to study its X-ray population and the conditions of thehot gas in its central region. We investigate the spectral properties ofthe discrete point-source population and give estimates of their X-rayspectral parameters. By analysing the RGS spectra, we derive temperatureand abundances for the hot gas located in its central region. A total ofsix X-ray point sources (four of them ULX candidates) were detected inthe energy range of 0.3-10.0 keV located within the galaxyD25 optical disk. Three of these sources are detected for thefirst time, and one of them, XMM-NGC2903 X2 with a luminosity of higherthan 1039 erg s-1. After fitting three differentmodels, we were able to estimate their luminosities, which arecompatible with those of binaries with a compact object in the form ofblack holes (BHs) rather than neutron stars (NSs). We extracted thecombined first-order RGS1 and RGS2 spectra of its central region, whichdisplay several emission lines. The spectrum is dominated by a strong Oviii Ly? emission line along with Ne x Ly? and several Fexvii features. The O vii complex is also significantly detected,although only the forbidden and resonance lines could be resolved. BothO vii f and r lines seem to be of similar strength, which is consistentwith the presence of the collisionally ionized gas that is typical ofstarburst galaxies. We fitted the spectrum to a model for a plasma incollisional ionization equilibrium (CIE) and the continuum was modelledwith a power law, resulting in a plasma temperature of T = 0.31 ±0.01 keV and an emission measure EM ? nHneV= 6.4-0.4+0.5 × 1061cm-3. We also estimated abundances that are consistent withsolar values.
| The dusty heart of nearby active galaxies. II. From clumpy torus models to physical properties of dust around AGN
With the possibilities of high spatial resolution imaging andspectroscopy as well as infrared (IR) interferometry, the dustyenvironments (= “dusty torus”) of active galactic nuclei(AGN) are now in reach of observations. Following our Paper I onground-based mid-IR spectro-photometry, we present an upgrade to ourradiative transfer model of three-dimensional clumpy dust tori. Theupgrade with respect to earlier work concerns an improved handling ofthe diffuse radiation field in the torus, which is approximated by astatistical approach. The models are presented as tools to translateclassical and interferometric observations into characteristicproperties of the dust distribution. We compare model spectral energydistributions (SEDs) for different chemical and grain-size compositionsof the dust and find that clouds with standard interstellar matter (ISM)dust and optical depth ?V ~ 50 appear in overallagreement with observed IR SEDs. By studying parameter dependencies, itis shown that type 1 AGN SEDs, in particular the mid-IR spectral index,can be used to constrain the radial dust cloud distribution power lawindex a, while other parameters are more difficult to assess using SEDsonly. Interferometry adds important additional information for modelingwhen it is interpreted concurrently with the SED. Although type 2 AGNcan in principle be used to constrain model parameters as well,obscuration effects make the analysis more ambiguous. We propose asimple, interferometry-based method to distinguish between“compact” and “extended” radial dustdistributions without detailed modeling of the data and introduce a wayto easily determine individual or sample average model parameters usingthe observed optical depth in the silicate feature and the mid-IRspectral index.
| A High Spatial Resolution Mid-Infrared Spectroscopic Study of the Nuclei and Star-Forming Regions in Luminous Infrared Galaxies
We present a high spatial (diffraction-limited) resolution (~0farcs3)mid-infrared (MIR) spectroscopic study of the nuclei and star-formingregions of four local luminous infrared galaxies (LIRGs) using T-ReCS onthe Gemini South telescope. We investigate the spatial variations of thefeatures seen in the N-band spectra of LIRGs on scales of ~100 pc, whichallow us to resolve their nuclear regions and separate the activegalactic nucleus (AGN) emission from that of the star formation (SF). Wecompare (qualitatively and quantitatively) our Gemini T-ReCS nuclear andintegrated spectra of LIRGs with those obtained with Spitzer IRS.Star-forming regions and AGNs show distinct features in the MIR spectra,and we spatially separate these, which is not possible using the Spitzerdata. The 9.7 μm silicate absorption feature is weaker in the nucleiof the LIRGs than in the surrounding regions. This is probably due tothe either clumpy or compact environment of the central AGN or young,nuclear starburst. We find that the [Ne II]12.81 μm luminositysurface density is tightly and directly correlated with that ofPaα for the LIRG star-forming regions (slope of 1.00 ±0.02). Although the 11.3 μm PAH feature shows also a trend withPaα, this is not common for all the regions and the slope issignificantly lower. We also find that the [Ne II]12.81 μm/Paαratio does not depend on the Paα equivalent width (EW), i.e., onthe age of the ionizing stellar populations, suggesting that, on thescales probed here, the [Ne II]12.81 μm emission line is a goodtracer of the SF activity in LIRGs. On the other hand, the 11.3 μmPAH/Paα ratio increases for smaller values of the Paα EW(increasing ages), indicating that the 11.3 μm PAH feature can alsobe excited by older stars than those responsible for the Paαemission. Finally, more data are needed in order to address thedifferent physical processes (age of the stellar populations, hardnessand intensity of the radiation field, mass of the star-forming regions)affecting the energetics of the polycyclic aromatic hydrocarbon featuresin a statistical way. Additional high spatial resolution observationsare essential to investigating the SF in local LIRGs at the smallestscales and determining ultimately whether they share the same physicalproperties as high-z LIRGs, ULIRGs, and submillimiter galaxies andtherefore belong to the same galaxy population.
| The Geometry of Mass Outflows and Fueling Flows in the Seyfert 2 Galaxy MRK 3
We present a study of the resolved emission-line regions and an innerdust/gas disk in the Seyfert 2 galaxy Mrk 3, based on Hubble SpaceTelescope observations. We show that the extended narrow-line region(ENLR), spanning ~4 kpc, is defined by the intersection of the ionizingbicone of radiation from the active galactic nucleus (AGN) and the innerdisk, which is not coplanar with the large-scale stellar disk. Thisintersection leads to different position and opening angles of the ENLRcompared to the narrow-line region (NLR). A number of emission-line arcsin the ENLR appear to be continuations of dust lanes in the disk,supporting this geometry. The NLR, which consists of outflowingemission-line knots spanning the central ~650 pc, is in the shape of abackward S. This shape may arise from rotation of the gas, or it maytrace the original fueling flow close to the nucleus that was ionizedafter the AGN turned on.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc. underNASA contract NAS 5-26555.
| VLT diffraction-limited imaging at 11 and 18?m of the nearest active galactic nuclei
Mid-infrared (mid-IR) imaging at resolutions of 300mas of the centralkpc region of 13 nearby, well-known active galaxies is presented. Thebulk of the mid-IR emission is concentrated on an unresolved centralsource within a size of less than 5-130pc, depending on the objectdistance. Further resolved emission is detected in 70 per cent of thesample in the form of circumnuclear star-forming rings or diffusenuclear extended emission. In the three cases with circumnuclear starformation, the stellar contribution is at least as important as that ofthe active galactic nuclei (AGN). In those with extended nuclearemission - a third of the sample - this emission represents a few percent of the total measured; however, this contribution may beunderestimated because of the chopped nature of these observations. Thisextended emission is generally collimated in a preferential directionoften coinciding with that of the extended ionized gas or the jet. InM87 and Cen A, where the emission extends along their respective jets,the emission is presumably synchrotron. In Circinus, NGC 1386 and NGC3783, it can be reconciled with thermal emission from dust heated atabout 100K by the active nucleus.In all cases, the nuclear fluxes measured at 11.8 and 18.7?mrepresent a minor contribution of the flux levels measured by largeaperture Infrared Astronomical Satellite (IRAS) data at the nearestenergy bands of 12 and 25?m. This contribution ranges from 30 percent to less than 10 per cent. In only three cases do the AGN fluxesagree with IRAS to within a factor of 2. In the AGN with strongcircumnuclear star formation, this component can well account for mostof the IRAS flux measured in these objects. But in all other cases,either a low surface brightness component extending over galactic scalesor strong extra-nuclear IR sources - e.g. HII regions in spiral arms -have to be the main source of the IRAS emission. In either case, thecontribution of these components dwarfs that of the AGN at mid-IRwavelengths.Based on observations collected at the European Southern Observatory,VLT programmes 076.B-0599, 077.B-0728.E-mail: reunanen@ftml.net (JR); aprieto@iac.es (MAP)
| Feeding versus feedback in NGC4151 probed with Gemini NIFS - II. Kinematics
We have used the Gemini Near-infrared Integral Field Spectrograph (NIFS)to map the gas kinematics of the inner ~200 × 500pc2 ofthe Seyfert galaxy NGC4151 in the Z, J, H and K bands at a resolvingpower of >=5000 and spatial resolution of ~8pc. The ionized gasemission is most extended along the known ionization bi-cone at positionangle PA = 60°-240°, but is observed also along its equatorialplane. This indicates that the active galactic nucleus (AGN) ionizes gasbeyond the borders of the bi-cone, within a sphere with ~1arcsec radiusaround the nucleus. The ionized gas has three kinematic components: (1)one observed at the systemic velocity and interpreted as originating inthe galactic disc; (2) one outflowing along the bi-cone, withline-of-sight velocities between -600 and 600kms-1 andstrongest emission at +/-(100-300)kms-1 and (3) anothercomponent due to the interaction of the radio jet with ambient gas. Theradio jet (at PA = 75°-255°) is not aligned with the narrow-lineregion (NLR) and produces flux enhancements mostly observed at thesystemic velocity, suggesting that the jet is launched close to theplane of the galaxy (approximately plane of the sky). The mass outflowrate, estimated to be ~1Msolaryr-1 along eachcone, exceeds the inferred black hole accretion rate by a factor of~100. This can be understood if the NLR is formed mostly by entrainedgas from the circumnuclear interstellar medium by an outflow probablyoriginating in the accretion disc. This flow represents feedback fromthe AGN, estimated to release a kinetic power of , which is only ~0.3per cent of the bolometric luminosity of the AGN.There is no evidence in our data for the gradual acceleration followedby gradual deceleration proposed by previous modelling of the [OIII]emitting gas. Our data allow the possibility that the NLR clouds areaccelerated close to the nucleus (within 0.1arcsec, which corresponds to~7 pc at the galaxy) after which the flow moves at essentially constantvelocity (~600kms-1), being consistent with near-infraredemission arising predominantly from the interaction of the outflow withgas in the galactic disc.The molecular gas exhibits distinct kinematics relative to the ionizedgas. Its emission arises in extended regions approximately perpendicularto the axis of the bi-cone and along the axis of the galaxy's stellarbar, avoiding the innermost ionized regions. It does not show anoutflowing component, being observed only at velocities very close tosystemic, and is thus consistent with an origin in the galactic plane.This hot molecular gas may only be the tracer of a larger reservoir ofcolder gas which represents the AGN feeding.
| Twelve years of X-ray and optical variability in the Seyfert galaxy NGC 4051
We discuss the origin of the optical variations in the narrow-lineSeyfert 1 galaxy NGC 4051 and present the results of a cross-correlationstudy using X-ray and optical light curves spanning more than 12 years.The emission is highly variable in all wavebands, and the amplitude ofthe optical variations is found to be smaller than that of the X-rays,even after correcting for the contaminating host galaxy flux fallinginside the photometric aperture. The optical power spectrum is bestdescribed by an unbroken power-law model with slope ? =1.4+0.6-0.2 and displays lower variability powerthan the 2-10keV X-rays on all time-scales probed. We find the lightcurves to be significantly correlated at an optical delay of1.2+1.0-0.3d behind the X-rays. This time-scale isconsistent with the light traveltime to the optical emitting region ofthe accretion disc, suggesting that the optical variations are driven byX-ray reprocessing. We show, however, that a model whereby the opticalvariations arise from reprocessing by a flat accretion disc cannotaccount for all the optical variability. There is also a secondsignificant peak in the cross-correlation function, at an optical delayof 39+2.7-8.4d. The lag is consistent with thedust sublimation radius in this source, suggesting that there is ameasurable amount of optical flux coming from the dust torus. We discussthe origin of the additional optical flux in terms of reprocessing ofX-rays and reflection of optical light by the dust.
| The spectral energy distribution of the central parsecs of the nearest AGN
Spectral energy distributions (SEDs) of the central few tens of parsecregion of some of the nearest, most well-studied, active galactic nuclei(AGN) are presented. These genuine AGN-core SEDs, mostly from Seyfertgalaxies, are characterized by two main features: an infrared (IR) bumpwith the maximum in the 2-10?m range and an increasing X-ray spectrumwith frequency in the 1 to ~200keV region. These dominant features arecommon to Seyfert type 1 and 2 objects alike. In detail, type 1 AGN areclearly distinguished from type 2 by their high spatial resolution SEDs:type 2 AGN exhibit a sharp drop shortwards of 2?m, with the opticalto UV region being fully absorbed; type 1s instead show a gentle 2?mdrop ensued by a secondary, partially absorbed optical to UV emissionbump. On the assumption that the bulk of optical to UV photons generatedin these AGN is reprocessed by dust and re-emitted in the IR in anisotropic manner, the IR bump luminosity represents >~70 per cent ofthe total energy output in these objects, and the second energeticallyimportant contribution is the high energies above 20keV.Galaxies selected by their warm IR colours, i.e. presenting a relativelyflat flux distribution in the 12-60?m range, have often beingclassified as AGN. The results from these high spatial resolution SEDsquestion this criterion as a general rule. It is found that theintrinsic shape of the infrared SED of an AGN and inferred bolometricluminosity largely depart from those derived from large aperture data.AGN luminosities can be overestimated by up to two orders of magnitudeif relying on IR satellite data. We find these differences to becritical for AGN luminosities below or about1044ergs-1. Above this limit, AGN tend to dominatethe light of their host galaxy regardless of the integration aperturesize used. Although the number of objects presented in this work issmall, we tentatively mark this luminosity as a threshold to identifygalaxy-light-dominated versus AGN-dominated objects.
| Radio structures of the nuclei of nearby Seyfert galaxies and the nature of the missing diffuse emission
We present archival high-spatial-resolution VLA and VLBA data of thenuclei of seven of the nearest and brightest Seyfert galaxies in theSouthern Hemisphere. At VLA resolution (~0.1arcsec), the nuclei of theSeyfert galaxies are unresolved, with the exception of MCG-5-23-16 andNGC7469, which show a core-jet structure. Three Seyfert nuclei aresurrounded by diffuse radio emission related to star-forming regions.VLBA observations with parsec-scale resolution demonstrate that inMRK1239 the nucleus is clearly resolved into two components separated by~30 pc, whereas the nucleus of NGC3783 is unresolved. Further comparisonbetween VLA and VLBA data of these two sources shows that the fluxdensity at parsec scales is only 20 per cent of that measured by theVLA. This suggests that the radio emission is not concentrated in asingle central component, as in elliptical radio galaxies, and anadditional low-surface-brightness component must be present. Acomparison of Seyfert nuclei with different radio spectra shows that the`presence' of undetected flux on a milliarcsecond scale is common insteep-spectrum objects, whereas in flat-spectrum objects essentially allthe radio emission is recovered. In the steep-spectrum objects, this`missing' flux probably results from non-thermal radiation related toactive galactic nuclei, perhaps from a jet that is disrupted in Seyfertgalaxies because of the denser environment of their spiral hosts.
| The Hard X-ray View of Reflection, Absorption, and the Disk-Jet Connection in the Radio-loud AGN 3C 33
We present results from Suzaku and Swift observations of the nearbyradio galaxy 3C 33, and investigate the nature of absorption,reflection, and jet production in this source. We model the 0.5-100 keVnuclear continuum with a power law that is transmitted either throughone or more layers of pc-scale neutral material, or through a modestlyionized pc-scale obscurer. The standard signatures of reflection from aneutral accretion disk are absent in 3C 33: there is no evidence of arelativistically blurred Fe Kα emission line, and no Comptonreflection hump above 10 keV. We find the upper limit to the neutralreflection fraction is R < 0.41 for an e-folding energy of 1 GeV. Weobserve a narrow, neutral Fe Kα line, which is likely to originateat least 2000 R s from the black hole. We show that theweakness of reflection features in 3C 33 is consistent with twointerpretations: either the inner accretion flow is highly ionized, orthe black-hole spin configuration is retrograde with respect to theaccreting material.
| Infrared Diagnostics for the Extended 12 μm Sample of Seyferts
We present an analysis of Spitzer IRS spectroscopy of 83 active galaxiesfrom the extended 12 μm sample. We find rank correlations betweenseveral tracers of star formation which suggest that (1) the polycyclicaromatic hydrocarbon feature is a reliable tracer of star formation, (2)there is a significant contribution to the heating of the cool dust bystars, and (3) the H2 emission is also primarily excited bystar formation. The 55-90 versus 20-30 spectral index plot is also adiagnostic of the relative contribution of starburst to active galacticnuclei (AGNs). We see there is a large change in spectral index acrossthe sample: Δα ~ 3 for both indices. Thus, the contributionto the IR spectrum from the AGN and starburst components can becomparable in magnitude but the relative contribution also varies widelyacross the sample. We find rank correlations between several AGNtracers. We find correlations of the ratios [O III]λ5007/[O IV]26 μm and [O III]λ5007/[Ne V] 14 μm with the silicatestrength which we adopt as an orientation indicator. This suggests thatsome of the [O III]λ5007 emission in these Seyferts is subject toorientation dependent obscuration as found by Haas et al. for radiogalaxies and quasars. There is no correlation of [Ne V] equivalent widthwith the silicate 10 μm strength, indicating that the [Ne V] emissionis not strongly orientation dependent. This suggests that the obscuringmaterial (e.g., torus) is not very optically thick at 14 μmconsistent with the results of Buchanan et al. We search forcorrelations between AGN and starburst tracers and we conclude that theAGN and starburst tracers are not correlated. This is consistent withour conclusion that the relative strength of the AGN and starburstcomponents varies widely across the sample. Thus, there is no simplelink between AGN fueling and black hole growth and star formation inthese galaxies. The density diagnostic [Ne V] 14/24 μm and [S III]18/33 μm line ratios are consistent with the gas being near the lowdensity limit, i.e., ~103 cm–3 for [Ne V]and ne ~ few hundred cm–3 for [S III]. Thedistribution of silicate 10 μm and 18 μm strengths is consistentwith the clumpy torus models of Sirocky et al. We find a rankcorrelation between the [Ne V] 14 μm line and the 6.7 μm continuumwhich may be due to an extended component of hot dust. The Sy 2's with ahidden broad-line region (HBLR) have a higher ratio of AGN-to-starburstcontribution to the spectral energy distribution than Sy 2's without anHBLR. This may contribute to the detection of the HBLR in polarizedlight. The Sy 2's with an HBLR are more similar to the Sy 1's than theyare to the Sy 2's without an HBLR.
| Infrared Excess sources: Compton thick QSOs, low-luminosity Seyferts or starbursts?
We explore the nature of Infrared Excess sources (IRX), which areproposed as candidates for luminous [LX(2-10 keV) >1043 erg s-1] Compton thick (NH > 2× 1024 cm-2) QSOs at z ~ 2. Lower redshift,z ~ 1, analogues of the distant IRX population are identified by firstredshifting to z = 2 the spectral energy distributions (SEDs) of allsources with secure spectroscopic redshifts in the AEGIS (6488) and theGOODS-North (1784) surveys and then selecting those that qualify as IRXsources at that redshift. A total of 19 galaxies are selected. The meanredshift of the sample is z ~ 1. We do not find strong evidence forCompton thick QSOs in the sample. For nine sources with X-raycounterparts, the X-ray spectra are consistent with Compton thin activegalactic nucleus (AGN). Only three of them show tentative evidence forCompton thick obscuration. The SEDs of the X-ray undetected populationare consistent with starburst activity. There is no evidence for a hotdust component at the mid-infrared associated with AGN heated dust. Ifthe X-ray undetected sources host AGN, an upper limit ofLX(2-10 keV) = 1043 erg s-1 isestimated for their intrinsic luminosity. We propose that a largefraction of the z ~ 2 IRX population is not Compton thick quasi-stellarobjects (QSOs) but low-luminosity [LX(2-10 keV) <1043 erg s-1], possibly Compton thin, AGN or dustystarbursts. It is shown that the decomposition of the AGN and starburstcontribution to the mid-IR is essential for interpreting the nature ofthis population, as star formation may dominate this wavelength regime.
| A new radio loudness diagnostic for active galaxies: a radio-to-mid-infrared parameter
We have studied the relationship between the nuclear (high-resolution)radio emission, at 8.4GHz (3.6cm) and 1.4GHz (20cm), the [OIV]?25.89 ?m, [NeIII] ?15.56 ?m and [NeII]?12.81 ?m emission lines and the black hole mass accretionrate for a sample of Seyfert galaxies. In order to characterize theradio contribution for the Seyfert nuclei we used the 8.4GHz/[OIV]ratio, assuming that [OIV] scales with the luminosity of the activegalactic nuclei (AGN). From this we find that Seyfert 1s (i.e. Seyfert1.0s, 1.2s and 1.5s) and Seyfert 2s (i.e. Seyfert 1.8s, 1.9s and 2.0s)have similar radio contributions, relative to the AGN. On the otherhand, sources in which the [NeII] emission is dominated either by theAGN or star formation have statistically different radio contributions,with star formation dominated sources more `radio loud', by a factor of~2.8 on average, than AGN dominated sources. We show that star formationdominated sources with relatively larger radio contribution have smallermass accretion rates. Overall, we suggest that 8.4GHz/[OIV], oralternatively, 1.4GHz/[OIV] ratios, can be used to characterize theradio contribution, relative to the AGN, without the limitation ofprevious methods that rely on optical observables.
| High-resolution X-ray spectroscopy and imaging of Mrk 573
We present a detailed analysis of the XMM-Newton Reflection GratingSpectrometer (RGS) high-resolution X-ray spectra of the Seyfert 2galaxy, Mrk 573. This analysis is complemented by the study of theChandra image and its comparison to optical (Hubble Space Telescope) andradio (Very Large Array) data. The soft X-ray emission is mainly due togas photoionized by the central active galactic nucleus, as indicated bythe detection of radiative recombination continua from OVII and OVIII aswell as by the prominence of the OVII forbidden line. This result isconfirmed by the best fit obtained with a self-consistent CLOUDYphotoionization model. However, a collisionally excited component isalso required, in order to reproduce the FeXVII lines, accounting forabout one-third of the total luminosity in the 15-26Å band. Oncethe same model in the Chandra Advanced CCD Imaging Spectrometer (ACIS)data is adopted, another photoionized component, with a higherionization parameter, is needed to take into account emission fromhigher Z metals. The broad-band ACIS spectrum also confirms theCompton-thick nature of the source. The imaging analysis shows the closemorphological correspondence between the soft X-ray and the [OIII]emission. The radio emission appears much more compact, although clearlyaligned with the narrow-line region. The collisional phase of the softX-ray emission may be due to starburst, requiring a star formation rateof ~=5-9Msolaryr-1, but there is no clear evidenceof this kind of activity from other wavelengths. On the other hand, itmay be related to the radio ejecta, responsible for the heating of theplasma interacting with the outflow, but the estimated pressure of thehot gas is much larger than the pressure of the radio jets, assumingequipartition and under reasonable physical parameters.
| X-ray Constraints on the Active Galactic Nuclei Properties in Spitzer-Infrared Spectrograph Identified z ~ 2 Ultraluminous Infrared Galaxies
We report Chandra X-ray constraints for 20 of the 52 high-redshiftultraluminous infrared galaxies (ULIRGs) identified in the SpitzerExtragalactic First Look Survey with f ν(24 μm)>0.9mJy, \log ({\nu f_{\nu }(24\,\mu m)\over \nu f_{\nu }(R)})>1, and\log ({\nu f_{\nu }(24\,\mu m)\over \nu f_{\nu }(8\,\mu m)})>0.5.Notably, decomposition of Spitzer mid-infrared IRS spectra for theentire sample indicates that they are comprised predominantly of weakpolycyclic aromatic hydrocarbon ULIRGs dominated by hot-dust continua,characteristic of active galactic nuclei (AGNs) activity. Given theirredshifts, they have AGN bolometric luminosities of≈1045-1047 erg s–1 comparableto powerful quasi-stellar objects (QSOs). This, coupled with their highIR-to-optical ratios and often significant silicate absorption, stronglyargues in favor of these mid-IR objects being heavily obscured QSOs.Here we use Chandra observations to further constrain their obscuration.At X-ray energies, we marginally detect two ULIRGs, while the rest haveonly upper limits. Using the IRS-derived 5.8 μm AGN continuumluminosity as a proxy for the expected X-ray luminosities, we find thatall of the observed sources must individually be highly obscured, whileX-ray stacking limits on the undetected sources suggest that themajority, if not all, are likely to be at least mildly Compton-thick (NH >~ 1024 cm–2). With a spacedensity of ≈1.4 × 10–7 Mpc–3at z ~ 2, such objects imply an obscured AGN fraction (i.e., the ratioof AGNs above and below N H = 1022cm–2) of gsim1.7:1 even among luminous QSOs. Given thatwe do not correct for mid-IR extinction effects and that our ULIRGselection is by no means complete for obscured AGNs, we regard ourconstraints as a lower limit to the true obscured fraction among QSOs atthis epoch. Our findings, which are based on extensive multi-wavelengthconstraints including Spitzer IRS spectra, should aid in theinterpretation of similar objects from larger or deeper mid-IR surveys,where considerable uncertainty about the source properties remains andcomparable follow-up is not yet feasible.
| Towards a complete census of active galactic nuclei in nearby galaxies: the incidence of growing black holes
We investigate the local supermassive black hole (SMBH) density functionand relative mass accretion rates of all active galactic nuclei (AGNs)identified in a volume-limited sample of infrared (IR) bright galaxies(LIR > 3 × 109Lsolar) to D< 15Mpc. A data base of accurate SMBH mass (MBH) estimatesis compiled from literature sources using physically motivated AGNmodelling techniques (reverberation mapping, maser mapping and gaskinematics) and well-established indirect MBH estimationmethods (the M-?* and MBH-LK,bulrelations). For the three sources without previously publishedMBH estimates, we use Two Micron All Sky Survey (2MASS)K-band imaging and GALFIT to constrain the bulge luminosities, and henceSMBH masses. In general, we find the AGNs in the sample host SMBHs whichare spread over a wide mass range [MBH ~ (0.1-30) ×107Msolar], but with the majority in the poorlystudied MBH ~ 106-107Msolarregion. Using sensitive hard X-ray (2-10keV) and mid-IR constraints wecalculate the bolometric luminosities of the AGNs (LBol,AGN)and use them to estimate relative mass accretion rates. We use thesedata to calculate the volume-averaged SMBH growth rate of galaxies inthe local Universe and find that the AGNs hosting SMBHs in the massrange MBH ~ 106-107Msolarare dominated by optically unidentified AGNs. These relatively smallSMBHs are acquiring a significant proportion of their mass in thepresent day, and are amongst the most rapidly growing in the localUniverse (SMBH mass-doubling times of ~6Gyr). Additionally, we findtentative evidence for an increasing volume-weighted AGN fraction withdecreasing SMBH mass in the MBH ~106-108Msolar range. Overall, weconclude that significant mass accretion on to small SMBHs may be missedin even the most sensitive optical surveys due to absent or weak opticalAGN signatures.
| Demystifying the coronal-line region of active galactic nuclei: spatially resolved spectroscopy with the Hubble Space Telescope
We present an analysis of Space Telescope Imaging Spectrograph(STIS)/Hubble Space Telescope optical spectra of a sample of 10 Seyfertgalaxies aimed at studying the structure and physical properties of thecoronal-line region (CLR). The high spatial resolution provided by STISallowed us to resolve the CLR and obtain key information about thekinematics of the CL gas, measure directly its spatial scale, and studythe mechanisms that drive the high-ionization lines. We find CLRsextending from just a few parsecs (pc) up to 230pc in radius, consistentwith the bulk of the coronal lines (CLs) originating between thebroad-line region and narrow-line region (NLR), and extending into theNLR in the case of [FeVII] and [NeV] lines. The CL profiles stronglyvary with the distance to the nucleus. We observed line splitting in thecore of some of the galaxies. Line peak shifts, both redshift andblueshift, typically reached 500kms-1, and even highervelocities (1000kms-1) in some of the galaxies. In general,CLs follow the same pattern of rotation curves as low-ionization lineslike [OIII]. From a direct comparison between the radio and the CLemission we find that neither the strength nor the kinematics of the CLsscales in any obvious and strong way with the radio jets. Moreover, thesimilarity of the flux distributions and kinematics of the CLs andlow-ionization lines, the low temperatures derived for the gas, and thesuccess of photoionization models to reproduce, within a factor of afew, the observed line ratios, point towards photoionization as the maindriving mechanism of CLs.
| Testing PDR models against ISO fine structure line data for extragalactic sources
Far-infrared [CII] 158-?m, [OI] 145-?m and [OI] 63-?m finestructure emission-line fluxes were measured from archival InfraredSpace Observatory Long Wavelength Spectrometer spectra of 46extragalactic sources, with 28 sources providing detections in all threelines. For 12 of the sources, the contribution to the [CII] 158-?mline flux from HII regions could be estimated from their detected [NII]122-?m line fluxes. The measured [CII]/[OI] and [OI] 63/145-?mline flux ratios were compared with those from a grid ofphotodissociation region (PDR) models previously computed using theUCL_PDR code. Persistent offsets between the observed and modelled lineratios could be partly attributed to the effects of [OI] 63-?mself-absorption. Using the Spherical Multi-Mol (SMMOL) code, wecalculated model [OI] line profiles and found that the strength of the[OI] 63-?m line was reduced by 20-80 per cent, depending on the PDRparameters. We conclude that high PDR densities and radiation fieldstrengths, coupled with the effects of [OI] 63-?m self-absorption,are likely to provide the best match to the observed line flux ratios.
| The Role of Starburst-Active Galactic Nucleus Composites in Luminous Infrared Galaxy Mergers: Insights from the New Optical Classification Scheme
We investigate the fraction of starbursts, starburst-active galacticnucleus (AGN) composites, Seyferts, and low-ionization narrowemission-line region galaxies (LINERs) as a function of infraredluminosity (L IR) and merger progress for ~500 infrared(IR)-selected galaxies. Using the new optical classifications affordedby the extremely large data set of the Sloan Digital Sky Survey, we findthat the fraction of LINERs in IR-selected samples is rare (<5%)compared with other spectral types. The lack of strong IR emission inLINERs is consistent with recent optical studies suggesting that LINERscontain AGN with lower accretion rates than in Seyfert galaxies. Mostpreviously classified IR-luminous LINERs are classified as starburst-AGNcomposite galaxies in the new scheme. Starburst-AGN composites appear to"bridge" the spectral evolution from starburst to AGN in ULIRGs. Therelative strength of the AGN versus starburst activity shows asignificant increase at high IR luminosity. In ULIRGs (L IR> 1012 L sun), starburst-AGN composite galaxiesdominate at early-intermediate stages of the merger, and AGN galaxiesdominate during the final merger stages. Our results are consistent withmodels for IR-luminous galaxies where mergers of gas-rich spirals fuelboth starburst and AGN, and where the AGN becomes increasingly dominantduring the final merger stages of the most luminous IR objects.
| High-resolution X-ray spectroscopy of the Seyfert 1 Mrk 841: insights into the warm absorber and warm emitter
Context. The Seyfert 1 galaxy Mrk 841 was observed five times between2001 and 2005 by the XMM-Newton X-ray observatory. The source is wellknown for showing spectral complexity in the variable iron line and inthe soft X-ray excess. Aims: The availability of multipleexposures obtained by the reflection grating spectrometer (RGS) camerasallows thorough study of the complex absorption and emission spectralfeatures in the soft X-ray band. This paper reports on the first studyof Mrk 841 soft X-ray spectrum at high spectral resolution. Methods: The three combined exposures obtained in January 2001 and thetwo obtained in January and July 2005 were analysed with the SPEXsoftware. Results: We detect a two-phase warm absorber. A mediumionisation component (log ? ~ 1.5-2.2 erg s cm-1) isresponsible for a deep absorption feature in the unresolved transitionarray of the Fe M-shell and for several absorption lines in the OVI-VIIIband, and a higher ionisation phase with log ? ~ 3 erg scm-1 is required to fit absorption in the NeIX-X band. Theionisation state and the column density of the gas present moderatevariation from 2001 to 2005 for both phases. The high ionisationcomponent of the warm absorber has no effect on the Fe K band. Nosignificant velocity shift of the absorption lines is measured in theRGS data. Remarkably, the 2005 spectra show emission features consistentwith photoionisation in a high-density (ne ?1011 cm-3) gas. A prominent OVII line triplet wasclearly observed in January 2005 and narrow radiative recombinationcontinua (RRC) of OVII and CVI were observed in both 2005 data sets. Abroad Gaussian line around 21.7 Å was also required to fit all thedata sets. The derived radial distance for the emission lines seems tosuggest that the photoionisation takes place within the optical broadline region of the source.
| The Palermo Swift-BAT hard X-ray catalogue. II. Results after 39 months of sky survey
Aims: We present the Palermo Swift-BAT hard X-ray catalogueobtained from the analysis of data acquired during the first 39 monthsof the Swift mission. Methods: We developed a dedicated softwareto perform the data reduction, mosaicking, and source detection of theBAT survey data. We analyzed the BAT dataset in three energy bands(14-150 keV, 14-30 keV, 14-70 keV), obtaining a list of 962 detectionsabove a significance threshold of 4.8 standard deviations. Theidentification of the source counterparts was pursued using threestrategies: cross-correlation with published hard X-ray catalogues,analysis of field observations of soft X-ray instruments, andcross-correlation with SIMBAD databases. Results: The surveycovers 90% of the sky down to a flux limit of 2.5×10-11 erg cm-2 s-1 and 50% ofthe sky down to a flux limit of 1.8 ×10-11 ergcm-2 s-1 in the 14-150 keV band. We derived acatalogue of 754 identified sources, of which ˜69% areextragalactic, ˜27% are Galactic objects, and ˜4% arealready known X-ray or gamma ray emitters, whose nature has yet to bedetermined. The integrated flux of the extragalactic sample is ˜1%of the cosmic X-ray background in the 14-150 keV range.Table 2 is also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/510/A48
| Characterizing the far-infrared properties of distant X-ray detected AGNs: evidence for evolution in the infrared-X-ray luminosity ratio
We investigate the far-infrared (FIR) properties of X-ray sourcesdetected in the Chandra Deep Field-South (CDF-S) survey using theultradeep 70 and 24 ?m Spitzer observations taken in this field.Since only 30 (i.e. ~10 per cent) of the 266 X-ray sources in the regionof the 70 ?m observations are detected at 70 ?m, we rely onstacking analyses of the 70 ?m data to characterize the average 70?m properties of the X-ray sources as a function of redshift, X-rayluminosity and X-ray absorption. Using Spitzer-IRS data of theSwift-Burst Alert Telescope (BAT) sample of z ~ 0 active galactic nuclei(AGNs), we show that the 70/24 ?m flux ratio can distinguish betweenAGN-dominated and starburst-dominated systems out to z ~ 1.5. Among theX-ray sources detected at 70 ?m, we note a large scatter in theobserved 70/24 ?m flux ratios, spanning almost a factor of 10 atsimilar redshifts, irrespective of object classification, suggesting arange of AGN:starburst ratios. From stacking analyses we find that theaverage observed 70/24 ?m flux ratios of AGNs out to an averageredshift of 1.5 are similar to z ~ 0 AGNs with similar X-rayluminosities (LX = 1042-44ergs-1) andabsorbing column densities (NH <=1023cm-2). Furthermore, both high-redshift and z ~0 AGNs follow the same tendency towards warmer 70/24 ?m colours withincreasing X-ray luminosity (LX). From analyses of theSwift-BAT sample of z ~ 0 AGNs, we note that the 70 ?m flux can beused to determine the IR (8-1000 ?m) luminosities of high-redshiftAGNs. We use this information to show that LX =1042-43ergs-1 AGNs at high redshifts (z = 1-2)have IR to X-ray luminosity ratios (LIR/LX) thatare, on average, 4.7+10.2-2.0 and12.7+7.1-2.6 times higher than AGNs with similarX-ray luminosities at z = 0.5-1 and ~0, respectively. By comparison, wefind that the LIR/LX ratios of LX =1043-44ergs-1 AGNs remain largely unchanged acrossthis same redshift interval. We explore the consequences that theseresults may have on the identification of distant, potentiallyCompton-thick AGNs using LIR/LX ratios. Inaddition, we discuss possible scenarios for the observed increase in theLIR/LX ratio with redshift, including changes inthe dust covering factor of AGNs and/or the star formation rates oftheir host galaxies. Finally, we show how deep observations to beundertaken by the Herschel Space Observatory will enable us todiscriminate between these proposed scenarios and also identifyCompton-thick AGNs at high redshifts.
| CHAMP+ observations of warm gas in M 17 SW
Context. Sub-millimeter and Far-IR observations have shown the presenceof a significant amount of warm (few hundred K) and dense(n(H_2)?10^4 cm-3) gas in sources ranging from activestar-forming regions to the vicinity of the Galactic center. Since themain cooling lines of the gas phase are important tracers of theinterstellar medium in Galactic and extragalactic sources, proper anddetailed understanding of their emission and the ambient conditions ofthe emitting gas, is necessary for a robust interpretation of theobservations. Aims: With high resolution (7''-9'') maps (3×3 pc2) of mid-J molecular lines we aim to probe thephysical conditions and spatial distribution of the warm (50 to severalhundred K) and dense gas (n(H_2)>10^5 cm-3) across theinterface region of the nearly edge-on M 17 SW nebula. Methods:We have used the dual color multiple pixel receiver CHAMP+ onthe APEX telescope to obtain a 5.3 arcmin×4.7 arcmin map of theJ=6?5 and J=7?6 transitions of 12CO, the13CO J=6?5 line, and the ^3P_2?{^3P_1} 370 ?mfine-structure transition of [C I] in M 17 SW. LTE and non-LTE radiativetransfer models are used to constrain the ambient conditions. Results: The warm gas extends up to a distance of 2.2 pc from the M 17SW ridge. The 13CO J=6?5 and [C I] 370 ?m lines havea narrower spatial extent of about 1.3 pc along a strip line atPA=63°. The structure and distribution of the [C I]^3P_2?{^3P_1} 370 ?m map indicate that its emission arises fromthe interclump medium with densities on the order of 10^3cm-3. Conclusions: The warmest gas is located alongthe ridge of the cloud, close to the ionization front. An LTEapproximation indicates that the excitation temperature of the embeddedclumps reaches 120 K. The non-LTE model suggests that the kinetictemperature at four selected positions cannot exceed 230 K in clumps ofa density of n(H_2)˜5×10^5 cm-3 and that the warm(T_k>100 K) and dense (n(H_2)?10^4 cm-3) gas traced bythe mid-J12CO lines represents just about 2% of the bulk ofthe molecular gas. The clump volume-filling factor ranges between 0.04and 0.11 at these positions.
| MAMBO observations at 240GHz of optically obscured Spitzer sources: source clumps and radio activity at high redshift
Optically very faint (R > 25.5) sources detected by the Spitzer SpaceTelescope at 24μm represent a very interesting population at redshiftz ~ (1.5-3). They exhibit strong clustering properties, implying thatthey are hosted by very massive haloes, and their mid-infrared emissioncould be powered by either dust-enshrouded star formation and/or by anobscured active galactic nucleus (AGN). We report observations carriedout with the Max Planck Millimetre Bolometer (MAMBO) array at the IRAM30-m antenna on Pico Veleta of a candidate protocluster with fiveoptically obscured sources selected from the 24-μm Spitzer sample ofthe First-Look Survey. Interestingly, these sources appear to lie on ahigh-density filament aligned with the two radio jets of an AGN. Fourout of five of the observed sources were detected. We combine thesemeasurements with optical, infrared and radio observations to probe thenature of the candidate protocluster members. Our preliminaryconclusions can be summarized as follows: the spectral energydistributions (SEDs) of all sources include both AGN and starburstcontributions; the AGN contribution to the bolometric luminositiesranges between 14 and 26 per cent of the total. Such a contribution isenough for the AGN to dominate the emission at 5.8, 8 and 24μm, whilethe stellar component, inferred from SED fitting, prevails at 1.25mm andat λ < 4.5μm. The present analysis suggests a coherentinterplay at high z between extended radio activity and the developmentof filamentary large-scale structures.
| On The Nuclear Obscuration of H2O Maser Galaxies
To shed light onto the circumnuclear environment of 22 GHz (λ ~1.3 cm) H2O maser galaxies, we have analyzed some of theirmultiwavelength properties, including the far-infrared luminosity (FIR),the luminosity of the [\rm O\,\mathsc{iii}]\lambda 5007 emission line,the nuclear X-ray luminosity, and the equivalent width (EW) of theneutral iron Kα emission line (EW (K α)). Ourstatistical analysis includes a total of 85 sources, most of themharboring an active galactic nucleus (AGN). There are stronganticorrelations between EW (K α) and two "opticalthickness parameters," i.e., the ratios of the X-ray luminosity versusthe presumably more isotropically radiated [\rm O\,\mathsc{iii}] and FIRluminosities. Based on these anticorrelations, a set of quantitativecriteria, EW (K α)>300 eV,L_{2\--10\keV}<2\L_[O\,\mathsc{iii]}, and L FIR>600 L2-10 keV can be established for Compton-thick nuclearregions. Eighteen H2O maser galaxies belong to this category.There are no obvious correlations between the EW (K α),the [\rm O\,\mathsc{iii}] luminosity, and the isotropic H2Omaser luminosity. When comparing samples of Seyfert 2s with and withoutdetected H2O maser lines, there seem to exist differences inEW (K α) and the fraction of Compton-thick nuclei. Thisshould be studied further. For AGN masers alone, there is no obviouscorrelation between FIR and H2O maser luminosities. However,including masers associated with star-forming regions, a linearcorrelation is revealed. Overall, the extragalactic FIR-H2Odata agree with the corresponding relation for Galactic maser sources,extrapolated by several orders of magnitude to higher luminosities.
| A Comparison of X-ray and Mid-Infrared Selection of Obscured Active Galactic Nuclei
We compare the relative merits of active galactic nuclei (AGNs)selection at X-ray and mid-infrared wavelengths using data frommoderately deep fields observed by both Chandra and Spitzer. TheX-ray-selected AGN sample and associated photometric and spectroscopicoptical follow-up are drawn from a subset of fields studied as part ofthe Serendipitous Extragalactic X-ray Source Identification (SEXSI)program. Mid-infrared data in these fields are derived from targeted andarchival Spitzer imaging, and mid-infrared AGN selection is accomplishedprimarily through application of the Infrared Array Camera (IRAC)color-color AGN "wedge" selection technique. Nearly all X-ray sources inthese fields which exhibit clear spectroscopic signatures of AGNactivity have mid-infrared colors consistent with IRAC AGN selection.These are predominantly the most luminous X-ray sources. X-ray sourcesthat lack high-ionization and/or broad lines in their optical spectraare far less likely to be selected as AGNs by mid-infrared colorselection techniques. The fraction of X-ray sources identified as AGNsin the mid-infrared increases monotonically as the X-ray luminosityincreases. Conversely, only 22% of mid-infrared-selected AGNs aredetected at X-ray energies in the moderately deep (langtexprang ≈ 100 ks) SEXSI Chandra data. We hypothesize thatIRAC sources with AGN colors that lack X-ray detections arepredominantly high-luminosity AGNs that are obscured and/or lie at highredshift. A stacking analysis of X-ray-undetected sources shows thatobjects in the mid-infrared AGN selection wedge have average X-rayfluxes in the 2-8 keV band 3 times higher than sources that fall outsidethe wedge. Their X-ray spectra are also harder. The hardness ratio ofthe wedge-selected stack is consistent with moderate intrinsicobscuration, but is not suggestive of a highly obscured, Compton-thicksource population. It is evident from this comparative study that inorder to create a complete, unbiased census of supermassive black holegrowth and evolution, a combination of sensitive infrared, X-ray, andhard X-ray selection is required. We conclude by discussing what sampleswill be provided by upcoming survey missions such as WISE, eROSITA, andNuSTAR.
| Type 2 Active Galactic Nuclei with Double-Peaked [O III] Lines: Narrow-Line Region Kinematics or Merging Supermassive Black Hole Pairs?
We present a sample of 167 type 2 active galactic nuclei (AGNs) withdouble-peaked [O III] λλ4959,5007 narrow emission lines,selected from the Seventh Data Release of the Sloan Digital Sky Survey.The double-peaked profiles can be well modeled by two velocitycomponents, blueshifted and redshifted from the systemic velocity. Halfof these objects have a more prominent redshifted component. In caseswhere the Hβ emission line is strong, it also shows two velocitycomponents whose line-of-sight (LOS) velocity offsets are consistentwith those of [O III]. The relative LOS velocity offset between the twocomponents is typically a few hundred km s-1, larger by afactor of ~1.5 than the line full width at half maximum of eachcomponent. The offset correlates with the host stellar velocitydispersion σ*. The host galaxies of this sample showsystematically larger σ*, stellar masses, andconcentrations, and older luminosity-weighted mean stellar ages than aregular type 2 AGN sample matched in redshift, [O III] λ5007equivalent width, and luminosity; they show no significant difference inradio properties. These double-peaked features could be due tonarrow-line region kinematics, or binary black holes. The statisticalproperties do not show strong preference for or against either scenario,and spatially resolved optical imaging, spectroscopy, radio or X-rayfollow-up are needed to draw firm conclusions.
| Radial Velocity Offsets Due to Mass Outflows and Extinction in Active Galactic Nuclei
We present a study of the radial velocity offsets between narrowemission lines and host galaxy lines (stellar absorption and H I 21 cmemission) in Seyfert galaxies with observed redshifts less than 0.043.We find that 35% of the Seyferts in the sample show [O III] emissionlines with blueshifts with respect to their host galaxies exceeding 50km s–1, whereas only 6% show redshifts this large, inqualitative agreement with most previous studies. We also find that agreater percentage of Seyfert 1 galaxies show blueshifts than Seyfert 2galaxies. Using Hubble Spce Talescope/Space Telescope ImagingSpectrograph spatially resolved spectra of the Seyfert 2 galaxy NGC 1068and the Seyfert 1 galaxy NGC 4151, we generate geometric models of theirnarrow-line regions (NLRs) and inner galactic disks, and show how thesemodels can explain the blueshifted [O III] emission lines in collapsedSTIS spectra of these two Seyferts. We conclude that the combination ofmass outflow of ionized gas in the NLR and extinction by dust in theinner disk (primarily in the form of dust spirals) is primarilyresponsible for the velocity offsets in Seyfert galaxies. More exoticexplanations are not needed. We discuss the implications of this resultfor the velocity offsets found in higher redshift active galacticnuclei.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc. underNASA contract NAS 5-26555.
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| The effectiveness of Mid IR / Far IR blind, wide area, spectral surveys in breaking the confusion limit.
Source confusion defines a practical depth to which to take large-areaextragalactic surveys. 3D imaging spectrometers with positional as wellas spectral information, however, potentially provide a means by whichto use line emission to break the traditional confusion limit. In thispaper we present the results of our investigation into the effectivenessof mid/far infrared, wide-area spectroscopic surveys in breaking theconfusion limit. We use SAFARI, a FIR imaging Fourier TransformSpectrometer concept for the proposed JAXA-led SPICA mission, as a testcase. We generate artificial skies representative of 100 SAFARIfootprints and use a fully-automated redshift determination method toretrieve redshifts for both spatially and spectrally confused sourcesfor bright-end and burst mode galaxy evolution models. We find we areable to retrieve accurate redshifts for 38/54% of the brightestspectrally confused sources, with continuum fluxes as much as an orderof magnitude below the 120 $\mu$m photometric confusion limit. Inaddition we also recover accurate redshifts for 38/29% of the secondbrightest spectrally confused sources. Our results suggest that deep,spectral line surveys with SAFARI can break the traditional photometricconfusion limit, and will also not only resolve, but provide redshiftsfor, a large number of previously inaccessible galaxies. To conclude wediscuss some of the limitations of the technique, as well as furtherwork.
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