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The AMIGA sample of isolated galaxies. II. Morphological refinement
We present a refinement of the optical morphologies for galaxies in theCatalog of Isolated Galaxies that forms the basis of the AMIGA (Analysisof the interstellar Medium of Isolated GAlaxies) project. Uniformreclassification using the digitized POSS II data benefited from thehigh resolution and dynamic range of that sky survey. Comparison withindependent classifications made for an SDSS overlap sample of more than200 galaxies confirms the reliability of the early vs. late-typediscrimination and the accuracy of spiral subtypes within Δ T =1-2. CCD images taken at the Observatorio de Sierra Nevada were alsoused to solve ambiguities in early versus late-type classifications. Aconsiderable number of galaxies in the catalog (n = 193) are flagged forthe presence of nearby companions or signs of distortion likely due tointeraction. This most isolated sample of galaxies in the local Universeis dominated by two populations: 1) 82% are spirals (Sa-Sd) with thebulk being luminous systems with small bulges (63% between types Sb-Sc)and 2) a significant population of early-type E-S0 galaxies (14%). Mostof the types later than Sd are low luminosity galaxies concentrated inthe local supercluster where isolation is difficult to evaluate. Thelate-type spiral majority of the sample spans a luminosity rangeMB-corr = -18 to -22 mag. Few of the E/S0 population are moreluminous than -21.0 marking the absence of the often-sought superL* merger (e.g. fossil elliptical) population. The rarity ofhigh luminosity systems results in a fainter derived M* forthis population compared to the spiral optical luminosity function(OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending onhow the sample is defined. This marks the AMIGA sample as unique amongsamples that compare early and late-type OLFs separately. In othersamples, which always involve galaxies in higher density environments,M^*_E/S0 is almost always 0.3-0.5 mag brighter than M^*_S, presumablyreflecting a stronger correlation between M* andenvironmental density for early-type galaxies.
| Massive star formation in the central regions of spiral galaxies
Context: . The morphology of massive star formation in the centralregions of galaxies is an important tracer of the dynamical processesthat govern the evolution of disk, bulge, and nuclear activity. Aims. Wepresent optical imaging of the central regions of a sample of 73 spiralgalaxies in the Hα line and in optical broad bands, and deriveinformation on the morphology of massive star formation. Methods. Weobtained images with the William Herschel Telescope, mostly at a spatialresolution of below one second of arc. For most galaxies, no Hαimaging is available in the literature. We outline the observing anddata reduction procedures, list basic properties, and present the I-bandand continuum-subtracted Hα images. We classify the morphology ofthe nuclear and circumnuclear Hα emission and explore trends withhost galaxy parameters. Results. We confirm that late-type galaxies havea patchy circumnuclear appearance in Hα, and that nuclear ringsoccur primarily in spiral types Sa-Sbc. We identify a number ofpreviously unknown nuclear rings, and confirm that nuclear rings arepredominantly hosted by barred galaxies. Conclusions. Other than instimulating nuclear rings, bars do not influence the relative strengthof the nuclear Hα peak, nor the circumnuclear Hα morphology.Even considering that our selection criteria led to an over-abundance ofgalaxies with close massive companions, we do not find any significantinfluence of the presence or absence of a close companion on therelative strength of the nuclear Hα peak, nor on the Hαmorphology around the nucleus.
| Conclusions of the workshop on the interferometric mode of OSIRIS
We present the conclusions of the workshop organized to define thescientific drivers and the derived main characteristics of high-orderscanning Fabry-Perot interferometers proposed to be coupled to OSIRIS atthe GTC.
| Diagnostics of the Ionized ISM: The Importance of Density Fluctuations
It is well known that when measuring electron densities in H II regionslocally via emission line ratios the values observed are 100cm-3, butgobal values obtained via emission measure using surface brightness asthe observed parameter are ~1cm-3. This difference is attributable todensity fluctuations,and traditional models for these is the ``Fillingfactor (FF)'' model, of Osterbrock and Flather. Implicit in this modelis the optical thinness of the fluctuations. We show here that if thesefluctuations are optically thick the diagnostic diagrams which are usedto find parameters, notably abundances, will be significantly affected.We present observational arguments supporting these ``clumpy'' models,and outline some initial results of their use.
| GHASP: an Hα kinematic survey of spiral and irregular galaxies - IV. 44 new velocity fields. Extension, shape and asymmetry of Hα rotation curves
We present Fabry-Perot observations obtained in the frame of the GHASPsurvey (Gassendi HAlpha survey of SPirals). We have derived the Hαmap, the velocity field and the rotation curve for a new set of 44galaxies. The data presented in this paper are combined with the datapublished in the three previous papers providing a total number of 85 ofthe 96 galaxies observed up to now. This sample of kinematical data hasbeen divided into two groups: isolated (ISO) and softly interacting(SOFT) galaxies. In this paper, the extension of the Hα discs, theshape of the rotation curves, the kinematical asymmetry and theTully-Fisher relation have been investigated for both ISO and SOFTgalaxies. The Hα extension is roughly proportional toR25 for ISO as well as for SOFT galaxies. The smallestextensions of the ionized disc are found for ISO galaxies. The innerslope of the rotation curves is found to be correlated with the centralconcentration of light more clearly than with the type or thekinematical asymmetry, for ISO as well as for SOFT galaxies. The outerslope of the rotation curves increases with the type and with thekinematical asymmetry for ISO galaxies but shows no special trend forSOFT galaxies. No decreasing rotation curve is found for SOFT galaxies.The asymmetry of the rotation curves is correlated with themorphological type, the luminosity, the (B-V) colour and the maximalrotational velocity of galaxies. Our results show that the brightest,the most massive and the reddest galaxies, which are fast rotators, arethe least asymmetric, meaning that they are the most efficient withwhich to average the mass distribution on the whole disc. Asymmetry inthe rotation curves seems to be linked with local star formation,betraying disturbances of the gravitational potential. The Tully-Fisherrelation has a smaller slope for ISO than for SOFT galaxies.
| BHαBAR: big Hα kinematical sample of barred spiral galaxies - I. Fabry-Perot observations of 21 galaxies
We present the Hα gas kinematics of 21 representative barredspiral galaxies belonging to the BHαBAR sample. The galaxies wereobserved with FaNTOmM, a Fabry-Perot integral-field spectrometer, onthree different telescopes. The three-dimensional data cubes wereprocessed through a robust pipeline with the aim of providing the mosthomogeneous and accurate data set possible useful for further analysis.The data cubes were spatially binned to a constant signal-to-noiseratio, typically around 7. Maps of the monochromatic Hα emissionline and of the velocity field were generated and the kinematicalparameters were derived for the whole sample using tilted-ring models.The photometrical and kinematical parameters (position angle of themajor axis, inclination, systemic velocity and kinematical centre) arein relative good agreement, except perhaps for the later-type spirals.
| Cool Gas and Massive Stars: The Nuclear Ring in M100
The SAURON integral-field spectrograph was used to observe the centralarea of the barred spiral galaxy M100 (NGC 4321). M100 contains anuclear ring of star formation, fueled by gas channeled inward by thegalaxy's bar. We present maps of emission-line strengths,absorption-line strength indices, and the gas velocity dispersion acrossthe field. The Hβ emission is strongest in the ring, along twocurved bar dust lanes and at the ends of the bar. The Mg babsorption-line strength shows a younger population of stars within thering than in the surrounding area. The gas velocity dispersion isnotably smaller than elsewhere in the field both in the ring and alongthe leading edge of the dust lanes. Low gas dispersion is correlatedspatially with the Hβ emission. We thus see stars being formed fromcold (low-dispersion) gas that is being channeled inward along the dustlanes under the influence of a large bar and accumulated into a ringnear the location of the inner Lindblad resonances. This lends furtherstrong support to the interpretation of nuclear rings in barred galaxiesas resonance phenomena.
| EGRET Upper Limits and Stacking Searches of Gamma-Ray Observations of Luminous and Ultraluminous Infrared Galaxies
We present a stacking analysis of EGRET γ-ray observations at thepositions of luminous and ultraluminous infrared galaxies. The latterwere selected from the recently presented HCN survey, which is thoughtto contain the most active star-forming regions of the universe.Different sorting criteria are used, and since there is no positivecollective detection of γ-ray emission from these objects, wedetermined both collective and individual upper limits. The uppermostexcess we find appears in the case of ULIRGs ordered by redshift, at avalue of 1.8 σ.
| CO in the Bipolar Radio Continuum Galaxy NGC 3367
CO(1-0) emission has been imaged at 2" resolution in the central 10 kpcof the barred spiral galaxy NGC 3367. This galaxy has bipolarsynchrotron lobes out to a radius of 6 kpc, straddling the compactnucleus. The peak molecular emission is in a source of radius 2" (425pc) centered on the galaxy nucleus. The molecular gas mass is~3×108 Msolar in this peak and~5.9×108 Msolar within a radius of 4.5" (950pc). The very large gas masses in the central source imply extinctionssufficiently high to completely obscure optical emission lines (e.g.,broad-line region) associated with the nuclear radio source. Theobserved Balmer lines probably originate in the narrow-line region a fewhundred parsecs from the nucleus. The CO emission in the central regionis elongated northeast-southwest, very similar to the position angle ofthe large-scale synchrotron lobes. This elongation is likely due to thenonaxisymmetric gravitational potential of the stellar bar. We inferthat the northeast radio continuum lobe is on the far side of the galaxyand the southwest lobe is on the near side. The central mass ofmolecular gas is of sufficient mass to power the active galactic nucleusaccretion luminosity for over 108 yr at 3 Msolaryr-1.
| The internal dynamical equilibrium of H II regions: A statistical study
We present an analysis of the integrated Hα emission line profilesfor the H SHAPE Ii region population of the spiral galaxies NGC 1530,NGC 6951 and NGC 3359. We show that 70% of the line profiles showtwo or three Gaussian components. The relations between the luminosity(log LHα) and non-thermal line width (logσnt) for the H SHAPE Ii regions of the three galaxiesare studied and compared with the relation found taken all the H SHAPEIi regions of the three galaxies as a single distribution. In all ofthese distributions we find a lower envelope in logσnt. A clearer envelope in σnt isfound when only those H SHAPE Ii regions with σnt>σs(13 km s-1) are considered, whereσs is a canonical estimate of the sound speed in theinterestellar medium. The linear fit for the envelope is logLHα =(36.8±0.7)+(2.0±0.5) logσnt where the Hα luminosity of the region istaken directly from a photometric H SHAPE Ii region catalogue. When theHα luminosity used instead is that fraction of the H SHAPE Iiregion luminosity, corresponding to the principal velocity component,i.e. to the turbulent non-expanding contribution, the linear fit is logLHα=(36.8±0.6)+(2.0±0.5) logσnt, i.e. unchanged but slightly tighter. The masses ofthe H SHAPE Ii regions on the envelope using the virial theorem and themass estimates from the Hα luminosity are comparable, whichoffers evidence that the H SHAPE Ii regions on the envelope arevirialized systems, while the remaining regions, the majority, are notin virial equilibrium.
| Expansive components in H II regions
We study the presence of low intensity high velocity components, whichwe have termed wing features in the integrated Hα emission lineprofiles of the H II region populations of the spiral barred galaxiesNGC 1530, NGC 3359 and NGC 6951. We find that more than a third of the HII region line profiles in each galaxy show these components. Thehighest fraction is obtained in the galaxy whose line profiles show thebest S:N, which suggests that wing features of this type may well existin most, if not all, H II region line profiles. Applying selectioncriteria to the wing features, we obtain a sample of H II regions withclearly defined high velocity components in their profiles.Deconvolution of a representative sample of the line profiles eliminatesany doubt that the wing features could possibly be due to instrumentaleffects. We present an analysis of the high velocity low intensityfeatures fitting them with Gaussian functions; the emission measures,central velocities and velocity dispersions for the red and bluefeatures take similar values. We interpret the features as signatures ofexpanding shells inside the H II regions. Up to a shell radius ofRshell 0.2 Rreg, the stellar winds from thecentral ionizing stars appear to satisfy the energy and momentumrequirements for the formation and driving the shell. Several examplesof the most luminous H II regions show that the shells appear to havelarger radii; in these cases additional mechanisms may well be needed toexplain the kinetic energies and momenta of the shells.
| Structure and star formation in disk galaxies. III. Nuclear and circumnuclear Hα emission
From Hα images of a carefully selected sample of 57 relativelylarge, Northern spiral galaxies with low inclination, we study thedistribution of the Hα emission in the circumnuclear and nuclearregions. At a resolution of around 100 parsec, we find that the nuclearHα emission in the sample galaxies is often peaked, andsignificantly more often so among AGN host galaxies. The circumnuclearHα emission, within a radius of two kpc, is often patchy inlate-type, and absent or in the form of a nuclear ring in early-typegalaxies. There is no clear correlation of nuclear or circumnuclearHα morphology with the presence or absence of a bar in the hostgalaxy, except for the nuclear rings which occur in barred hosts. Thepresence or absence of close bright companion galaxies does not affectthe circumnuclear Hα morphology, but their presence does correlatewith a higher fraction of nuclear Hα peaks. Nuclear rings occur inat least 21% (±5%) of spiral galaxies, and occur predominantly ingalaxies also hosting an AGN. Only two of our 12 nuclear rings occur ina galaxy which is neither an AGN nor a starburst host. We confirm thatweaker bars host larger nuclear rings. The implications of these resultson our understanding of the occurrence and morphology of massive starformation, as well as non-stellar activity, in the central regions ofgalaxies are discussed.
| Nuclear spirals in galaxies: gas response to an asymmetric potential - II. Hydrodynamical models
Nuclear spirals naturally form as a gas response to non-axisymmetry inthe galactic potential, even if the degree of this asymmetry is verysmall. Linear wave theory well describes weak nuclear spirals, butspirals induced by stronger asymmetries in the potential are clearlybeyond the linear regime. Hydrodynamical models indicate spiral shocksin this latter case that, depending on how the spiral intersects thex2 orbits, either get damped, leading to the formation of thenuclear ring, or get strengthened, and propagate towards the galaxycentre. A central massive black hole of sufficient mass can allow thespiral shocks to extend all the way to its immediate vicinity, and togenerate gas inflow up to 0.03 Msolar yr-1, whichcoincides with the accretion rates needed to power luminous local activegalactic nuclei.
| A molecular face-on view of the Galactic Centre region
We present a method to derive positions of molecular clouds along thelines of sight from a quantitative comparison between 2.6-mm CO emissionlines and 18-cm OH absorption lines, and apply it to the centralkiloparsecs of the Milky Way. With some simple but justifiableassumptions, we derive a face-on distribution of the CO brightness andcorresponding radial velocity in the Galactic Centre without any help ofkinematical models. The derived face-on distribution of the gas iselongated and inclined so that the Galactic-eastern (positive longitude)side is closer to us. The gas distribution is dominated by a bar-likecentral condensation, whose apparent size is 500 × 200 pc. A ridgefeature is seen to stretch from one end of the central condensation,though its elongated morphology might be artificial. The velocity fieldshows clear signs of non-circular motion in the central condensation.The `expanding molecular ring' feature corresponds to the peripheralregion surrounding the central condensation, with the Galactic-easternend being closer to us. These characteristics agree with a picture inwhich the kinematics of the gas in the central kiloparsec of the Galaxyis under the strong influence of a barred potential. The face-ondistribution of the in situ pressure of the molecular gas is derivedfrom the CO multiline analysis. The derived pressure is found to behighest in the central 100 pc. In this region, the gas is accumulatingand is forming stars.
| Determination of the Thickness of Non-Edge-on Disk Galaxies
We propose a method to determine the thickness of non-edge-on diskgalaxies from their observed structure of spiral arms, based on thesolution of the truly three-dimensional Poisson's equation for alogarithmic disturbance of density and under the condition where theself-consistency of the density wave theory is no longer valid. Fromtheir measured number of arms, pitch angle and location of the innermostpoint of the spiral arms, we derive and present the thicknesses of 34spiral galaxies.
| The Star Formation Rate and Dense Molecular Gas in Galaxies
HCN luminosity is a tracer of dense molecular gas,n(H2)>~3×104cm-3, associatedwith star-forming giant molecular cloud (GMC) cores. We present theresults and analysis of our survey of HCN emission from 65 infraredgalaxies, including nine ultraluminous infrared galaxies (ULIGs,LIR>~1012Lsolar), 22 luminousinfrared galaxies (LIGs,1011Lsolar0.06 are LIGs or ULIGs. Normal spiralsall have similar and low dense gas fractionsLHCN/LCO=0.02-0.05. The global star formationefficiency depends on the fraction of the molecular gas in a densephase.
| A Search for Kinematic Evidence of Radial Gas Flows in Spiral Galaxies
CO and H I velocity fields of seven nearby spiral galaxies, derived fromradio-interferometric observations, are decomposed into Fouriercomponents whose radial variation is used to search for evidence ofradial gas flows. Additional information provided by optical ornear-infrared isophotes is also considered, including the relationshipbetween the morphological and kinematic position angles. To assist ininterpreting the data, we present detailed modeling that demonstratesthe effects of bar streaming, inflow, and a warp on the observed Fouriercomponents. We find in all of the galaxies evidence for eitherelliptical streaming or a warped disk over some range in radius, withdeviations from pure circular rotation at the level of ~20-60 kms-1. Evidence for kinematic warps is observed in severalcases well inside R25. No unambiguous evidence for radialinflows is seen in any of the seven galaxies, and we are able to placean upper limit of ~5-10 km s-1 (3%-5% of the circular speed)on the magnitude of any radial inflow in the inner regions of NGC 4414,NGC 5033, and NGC 5055. We conclude that the inherent nonaxisymmetry ofspiral galaxies is the greatest limitation to the direct detection ofradial inflows.
| Gravitational Bar and Spiral Arm Torques from Ks-band Observations and Implications for the Pattern Speeds
We have obtained deep near-infrared Ks-band William HerschelTelescope observations of a sample of 15 nearby spiral galaxies having arange of Hubble types and apparent bar strengths. The near-infraredlight distributions are converted into gravitational potentials, and themaximum relative gravitational torques due to the bars and the spiralsare estimated. We find that spiral strength, Qs, and barstrength, Qb, correlate well with other measures of spiralarm and bar amplitudes and that spiral and bar strengths also correlatewell with each other. We also find a correlation between the positionangle of the end of the bar and the position angle of the inner spiral.These correlations suggest that the bars and spirals grow together withthe same rates and pattern speeds. We also show that the strongest barstend to have the most open spiral patterns. Because open spirals implyhigh disk-to-halo mass ratios, bars and spirals most likely growtogether as a combined disk instability. They stop growing for differentreasons, however, giving the observed variation in bar-spiralmorphologies. Bar growth stops because of saturation when most of theinner disk is in the bar, and spiral growth stops because of increasedstability as the gas leaves and the outer disk heats up.
| Propagation of ionizing radiation in H II regions: The effects of optically thick density fluctuations
The accepted explanation of the observed dichotomy of two orders ofmagnitude between in situ measurements of electron density in H IIregions, derived from emission line ratios, and average measurementsbased on integrated emission measure, is the inhomogeneity of theionized medium. This is expressed as a ``filling factor", the volumeratio of dense to tenuous gas, measured with values of order10-3. Implicit in the filling factor model as normally used,is the assumption that the clumps of dense gas are optically thin toionizing radiation. Here we explore implications of assuming thecontrary: that the clumps are optically thick. A first consequence isthe presence within H II regions of a major fraction of neutralhydrogen. We estimate the mean Ho/H+ ratio for apopulation of H II regions in the spiral galaxy NGC 1530 to be the orderof 10, and support this inference using dynamical arguments. Theoptically thick clumpy models allow a significant fraction of thephotons generated by the ionizing stars to escape from their H IIregion. We show, by comparing model predictions with observations, thatthese models give an account at least as good as, and probably betterthan that of conventional models, of the radial surface brightnessdistribution and of selected spectral line diagnostics for physicalconditions within H II regions. These models explain how an H SHAPE Iiregion can appear, from its line ratios, to be ionization bounded, yetpermit a major fraction of its ionizing photons to escape.
| Ionized gas kinematics and massive star formation in NGC 1530
We present emission line mapping of the strongly barred galaxy NGC 1530obtained using Fabry-Pérot interferometry in H\alpha, atsignificantly enhanced angular resolution compared with previouslypublished studies. The main point of the work is to examine in detailthe non-circular components of the velocity field of the gas, presumablyinduced by the strongly non-axisymmetric gravitational potential of thebar. To do this we first derive a model rotation curve making minimumassumptions about kinematic symmetry, and go on to measure thenon-circular component of the full radial velocity field. This clearlyreveals the streaming motions associated with the spiral density waveproducing the arms, and the quasi-elliptical motions with speeds oforder 100 km s-1 aligned with the bar. It also shows in somedetail how these flows swing in towards and around the nucleus as theycross a circumnuclear resonance, from the dominant ``x1orbits" outside the resonance to ``x2 orbits" within it.Comparing cross-sections of this residual velocity map along and acrossthe bar with the surface brightness map in Hα indicates asystematic offset between regions of high non-circular velocity andmassive star formation. To investigate further we produce maps ofvelocity gradient along and across the bar. These illustrate verynicely the shear compression of the gas, revealed by the location of thedust lanes along loci of maximum velocity gradient perpendicular to thebar. They also show clearly how shear, seen in our data as velocitygradient perpendicular to the flow, acts to inhibit massive starformation, whereas shocks, seen as strong velocity gradients along theflow vector, act to enhance it. Although the inhibiting effect of gasshear flow on star formation has long been predicted, this is theclearest observational illustration so far of the effect, thanks to thestrong shock-induced counterflow system in the bar. It is also theclearest evidence that dust picks out shock-induced inflow along bars.These observations should be of considerable interest to those modellingmassive star formation in general.
| Fourier Analysis of a Spiral Galaxies Sample: Determination of Kinematic and Morphological Parameters
We present partial results of a larger work searching for corotations ina large sample of grand design spiral galaxies. We have searched forcorotation resonances (CRs) in five northern spiral galaxies: NGC 266,NGC 1520, NGC 1530, NGC 2543, and NGC 7479. We can reject some detectedCRs values in those galaxies when we perceive dust lanes in bars, we canasociate the (CR) with local features or simply there is a lowsignal-noise in these regions. We have detected two CRs in NGC 2543 andNGC 7479. Using the 2D Fourier technique we have determined the mainspectrum components for the spiral pattern and the pitch angles of thespiral arms for 19 galaxies of our sample. In all the galaxies the m=2mode is the most important one. However, we have detected the presenceof strong m=3 modes in five galaxies of our sample (NGC 151, NGC 1241,NGC 4254, NGC 5427, and NGC 7753). We did not find correlation betweenthe main pitch angle of the galaxies and the morphological type.
| Physical Scenarios for Supersonic Gas Flows Observed in H II Regions
Line profiles in ensuremath {{H}alpha } emission from H II regionpopulations in spiral galaxies show emission features at +/-50 km/sfrom the main emission peaks of a significant fraction of regions, whichare characteristic of expanding shells. We interpret these in twopossible scenarios: mass-loaded wind outflows from the central OB stars,or dust-coupled, radiation-driven outflows, caused by the same objects.
| Observations of Massive Supersonic Outflows in Highly Luminous H II Regions
Using H alpha emission line profiles we detect outflowing ionized gasat velocities of order 50 km/s from representative luminous H II regionsin two sample disk galaxies, NGC 3359 and NGC 1530, and calculate thephysical parameters of the outflowing material.
| Aperture Synthesis CO(J=1--0) Observations and Near-Infrared Photometry of the Non-Barred Seyfert Galaxy NGC 5033
Aperture synthesis observations of CO(J = 1 -- 0) emission andnear-infrared broad-band photometry of the non-barred Seyfert galaxy NGC5033 (D = 18.7 Mpc) were performed. Our 3".9 × 3".6 resolution COobservations reveal a perturbed distribution and the kinematics ofmolecular gas in the center of NGC 5033; we find the characteristicgaseous features that are widely observed in barred spiral galaxies,such as two bright CO peaks near the center (separated by 3" or270pc from the nucleus), two offset ridges of CO emission emanating fromthe CO peaks, and a CO ring (with a radius of 14" or 1.3kpc).Double-peaked velocity profiles are also evident near the two CO peaks,implying that these CO peaks are orbit crowding zones in a barred/ovalpotential. Although NIR data only give an upper limit of the possiblebar lengths due to a large inclination of the NGC 5033 disk (i =68°), our CO data clearly suggests the presence of a small (thesemi-major axis of about 12" -- 15" or 1.1-1.4kpc) nuclear bar (or ovalstructure) in the center of the ``non-barred'' galaxy NGC 5033. Ourresults demonstrate that high-resolution CO imaging-spectroscopy isuseful to search for nuclear bars, even in highly inclined systems whereisophoto fitting techniques are not applicable. We find that the gasmass-to-dynamical mass ratio, Mgas/Mdyn, is small(≤ 1%) within a radius of 2" or 180pc, in contrast to starburstnuclei. This implies that the starburst does not cohabitate in thetype-1.5 Seyfert nucleus of NGC 5033.
| INGRID: A near-infrared camera for the William Herschel Telescope
Rapid developments in near-infrared (NIR) arrays and adaptive opticssystems have driven the development of wide-field andhigh-spatial-resolution, high-optical-quality NIR imagers andspectrographs, providing an unparalleled boost to NIR observations.Based around a 1024 × 1024 pixel2 Hawaii-1 array, theIsaac Newton Group Red Imaging Device (INGRID) imager provides a fieldof view >16 arcmin2 (at the Cassegrain focus) whilstNyquist sampling the median summer seeing disc. When used in conjunctionwith the Nasmyth Adaptive Optics for Multi-Purpose Instrumentation(NAOMI) system and a second set of collimation optics, a high spatialresolution mode (0.04 arcsec pixel-1) is offered, providingnear-diffraction-limited imaging. INGRID uses an all-refractive designand employs a cold stop to reduce thermal background emission, criticalto the performance as it is used on the non-infrared optimized 4.2-mWilliam Herschel Telescope (WHT). We discuss the design and operation ofINGRID and illustrate its performance by discussing commissioningobservations of the cluster Abell 2218 and the spiral galaxies NGC 3351and 1530.
| First results from the HI Jodrell All Sky Survey: inclination-dependent selection effects in a 21-cm blind survey
Details are presented of the HI Jodrell All Sky Survey (HIJASS). HIJASSis a blind neutral hydrogen (HI) survey of the northern sky (δ> 22°), being conducted using the multibeam receiver on theLovell Telescope (full width at half-maximum beamwidth 12 arcmin) atJodrell Bank. HIJASS covers the velocity range -3500 to 10 000 kms-1, with a velocity resolution of 18.1 km s-1 andspatial positional accuracy of ~2.5 arcmin. Thus far about 1115deg2 of sky have been surveyed. The average rms noise duringthe early part of the survey was around 16 mJy beam-1.Following the first phase of the Lovell Telescope upgrade (in 2001), therms noise is now around 13 mJy beam-1. We describe themethods of detecting galaxies within the HIJASS data and of measuringtheir HI parameters. The properties of the resulting HI-selected sampleof galaxies are described. Of the 222 sources so far confirmed, 170 (77per cent) are clearly associated with a previously catalogued galaxy. Afurther 23 sources (10 per cent) lie close (within 6 arcmin) to apreviously catalogued galaxy for which no previous redshift exists. Afurther 29 sources (13 per cent) do not appear to be associated with anypreviously catalogued galaxy. The distributions of peak flux, integratedflux, HI mass and cz are discussed. We show, using the HIJASS data, thatHI self-absorption is a significant, but often overlooked, effect ingalaxies with large inclination angles to the line of sight. Properlyaccounting for it could increase the derived HI mass density of thelocal Universe by at least 25 per cent. The effect that this will haveon the shape of the HI mass function will depend on how self-absorptionaffects galaxies of different morphological types and HI masses. We alsoshow that galaxies with small inclinations to the line of sight may alsobe excluded from HI-selected samples, since many such galaxies will haveobserved velocity widths that are too narrow for them to bedistinguished from narrow-band radio-frequency interference. This effectwill become progressively more serious for galaxies with smallerintrinsic velocity widths. If, as we might expect, galaxies with smallerintrinsic velocity widths have smaller HI masses, then compensating forthis effect could significantly steepen the faint-end slope of thederived HI mass function.
| Vertical Scale Parameter Estimates for 48 Non-edge-on Spiral Galaxies
In the first paper of this series, we directly studied the mathematicalforms, symmetry of spiral structure, and the projection of galacticdiscs on the images, and measured the pitch angles of the spiral armsand inclination angles of the galactic discs for 60 spiral galaxies. Inthis second paper, we estimate the vertical scale parameters of 48non-edge-on spiral galaxies based on the method proposed by Peng et al.and on the results given in Paper I. As we know, for edge-on discgalaxies we can obtain the vertical scale parameter from the photometry,once a mathematical form is specified for the vertical lightdistribution. For non-edge-on galaxies, some other methods have to beused. The statistical result was that the vertical scale parameter iscomparable for edge-on and non-edge-on galaxies, although it is obtainedfrom two very different methods.
| Circumnuclear Dust in Nearby Active and Inactive Galaxies. II. Bars, Nuclear Spirals, and the Fueling of Active Galactic Nuclei
We present a detailed study of the relation between circumnuclear dustmorphology, host-galaxy properties, and nuclear activity in nearbygalaxies. We use our sample of 123 nearby galaxies withvisible-near-infrared color maps from the Hubble Space Telescope tocreate well-matched, ``paired'' samples of 28 active and 28 inactivegalaxies, as well as 19 barred and 19 unbarred galaxies, that have thesame host-galaxy properties. Comparison of the barred and unbarredgalaxies shows that grand-design nuclear dust spirals are found only ingalaxies with a large-scale bar. These nuclear dust spirals, which arepresent in approximately one-third of all barred galaxies, also appearto be connected to the dust lanes along the leading edges of thelarge-scale bars. Grand-design nuclear spirals are more common thaninner rings, which are present in only a small minority of the barredgalaxies. Tightly wound nuclear dust spirals, in contrast, show a strongtendency to avoid galaxies with large-scale bars. Comparison of theactive galactic nuclei (AGNs)and inactive samples shows that nucleardust spirals, which may trace shocks and angular momentum dissipation inthe interstellar medium, occur with comparable frequency in both activeand inactive galaxies. The only difference between the active andinactive galaxies is that several inactive galaxies appear to completelylack dust structure in their circumnuclear region, while none of theAGNs lack this structure. The comparable frequency of nuclear spirals inactive and inactive galaxies, combined with previous work that finds nosignificant difference in the frequency of bars or interactions betweenwell-matched active and inactive galaxies, suggests that no universalfueling mechanism for low-luminosity AGNs operates at spatial scalesgreater than a ~100 pc radius from the galactic nuclei. The similaritiesof the circumnuclear environments of active and inactive galaxiessuggest that the lifetime of nuclear activity is less than thecharacteristic inflow time from these spatial scales. Anorder-of-magnitude estimate of this inflow time is the dynamicaltimescale. This sets an upper limit of several million years to thelifetime of an individual episode of nuclear activity.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.
| The IRAS Revised Bright Galaxy Sample
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
| A Technique for Separating the Gravitational Torques of Bars and Spirals in Disk Galaxies
We describe a Fourier-based method of separating bars from spirals innear-infrared images. The method takes advantage of the fact that a baris typically a feature with a relatively fixed position angle and usesthe simple assumption that the relative Fourier amplitudes due to thebar decline with radius past a maximum in the same or a similar manneras they rose to that maximum. With such an assumption, the bar can beextrapolated into the spiral region and removed from an image, leavingjust the spiral and the axisymmetric background disk light. We refer tosuch a bar-subtracted image as the ``spiral plus disk'' image. Theaxisymmetric background (Fourier index m=0 image) can then be added backto the bar image to give the ``bar plus disk'' image. The procedureallows us to estimate the maximum gravitational torque per unit mass perunit square of the circular speed for the bar and spiral forcingseparately, parameters that quantitatively define the bar strengthQb and the spiral strength Qs following the recentstudy of Buta & Block. For the first time, we are able to measurethe torques generated by spiral arms alone, and we can now define spiraltorque classes, in the same manner as bar torque classes are delineated.We outline the complete procedure here using a 2.1 μm image of NGC6951, a prototypical SAB(rs)bc spiral having an absolute blue magnitudeof -21 and a maximum rotation velocity of 230 km s-1.Comparison between a rotation curve predicted from the m=0 near-infraredlight distribution and an observed rotation curve suggests that NGC 6951is maximum disk in its bar and main spiral region, implying that ourassumption of a constant mass-to-light ratio in our analysis is probablyreliable. We justify our assumption on how to make the bar extrapolationusing an analysis of NGC 4394, a barred spiral with only weaknear-infrared spiral structure, and we justify the number of neededFourier terms using NGC 1530, one of the most strongly barred galaxies(bar class 7) known. We also evaluate the main uncertainties in thetechnique. Allowing for uncertainties in vertical scale height, barextrapolation, sky subtraction, orientation parameters, and theasymmetry in the spiral arms themselves, we estimateQb=0.28+/-0.04 and Qs=0.21+/-0.06 for NGC 6951.
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