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Gas in early-type galaxies: cross-fuelling in late-type-early-type pairs?
We present 12CO (J= 1-0) and 12CO (J= 2-1)observations of eight early-type galaxies, forming part of a sample ofinteracting galaxies, each consisting of one late- and one early-typesystem. All of the early-type galaxies observed are undetected in CO tolow levels, allowing us to place tight constraints on their moleculargas content. Additionally, we present HI absorption data for one system.The implications for possible gas transfer from the late- to theearly-type galaxy during the interaction are discussed.
| X-ray obscuration and obscured AGN in the local universe
We discuss the X-ray properties of 49 local (z<0.035) Seyfert 2galaxies with HST/WFC2 high-resolution optical coverage. It includes theresults of 26 still unpublished Chandra and XMM-Newton observations,which yield 25 (22) new X-ray detections in the 0.5-2 keV (2-10 keV)energy band. Our sample covers a range in the 2-10 keV observed flux,F2-10, from 3 × 10-11 to 6 ×10-15 erg cm-2 s-1. The percentage ofobjects that are likely obscured by Compton-thick matter (columndensity, NH ≥ σt-1 ≃1.6 × 1024 cm-2) is ≃50%, and reaches≃80% for log (F2-10) < 12.3. Hence, Kαfluorescent iron lines with large Equivalent Width ({EW} > 0.6 keV)are common in our sample (6 new detections at a confidence level≥2σ). They are explained as due to reflection off theilluminated side of optically thick material. We confirm a correlationbetween the presence of a 100-pc scale nuclear dust in the WFC2 imagesand Compton-thin obscuration. We interpret this correlation as due tothe large covering fraction of gas associated with the dust lanes. TheX-ray spectra of highly obscured AGN invariably present a prominent softexcess emission above the extrapolation of the hard X-ray component.This soft component can account for a very large fraction of the overallX-ray energy budget. As this component is generally unobscured - andtherefore likely produced in extended gas structures - it may lead to asevere underestimation of the nuclear obscuration in z 1 absorbedAGN, if standard X-ray colors are used to classify them. As a by-productof our study, we report the discovery of a soft X-ray, luminous(≃7 × 1040 erg s-1) halo embedding theinteracting galaxy pair Mkn 266.
| On the Observed Rapid Motions in Extragalactic Radio Sources
Using interferometric methods, radio astronomers have shown that veryrapid motions involving radio jets are detectable in a variety of activecenters: the nuclei of low-redshift radio galaxies, QSOs and BL Lacobjects, and active binary systems containing a black hole or a neutronstar in our own Galaxy. By comparing the positions of about 80extragalactic sources of this type with the position of the galaxies inthe de Vaucouleurs catalog and the updated QSO catalog ofVéron-Cetty and Véron, it is shown that about 50% of themlie within 1° of a low-redshift spiral galaxy, and about 15% lie soclose to galaxies (Δθ<=10') that theassociations are highly significant. Thus, the sources are probablyphysically associated with these galaxies. All the galaxies areclassified as spiral. In addition, many of the sources have other QSOslying very close to them. These results suggest that the motionsobserved in these radio sources, as well as in the nuclei of radiogalaxies and in Galactic microquasars, and perhaps in many more QSOs andother objects, are all similar and are mildly relativistic, and they donot require us to invoke large Lorentz factors. Some of the problemsassociated with this picture are discussed.
| Ongoing Mass Transfer in the Interacting Galaxy Pair NGC 1409/1410
I present two-band Hubble Space Telescope (HST) STIS imaging and WIYNspectral mapping of ongoing mass transfer in the interacting galaxy pairNGC 1409/1410 (where NGC 1410 is the Seyfert galaxy also cataloged asIII Zw 55). Archival snapshot WFPC2 imaging from the survey by Malkanand coworkers showed a dust feature stretching between the galaxies,apparently being captured by NGC 1409. The new images allow estimates ofthe mass being transferred and the rate of transfer. An absorption lanetypically 0.25" (100 pc) wide, with a representative optical depthτB=0.2, cuts across the spiral structure of NGC 1410,crosses the 7 kpc projected space between the nuclei, wraps in front ofand, at the limits of detection, behind NGC 1409 and becomes a denser(τB=0.4) polar feature around the core of NGC 1409. Thecombination of extinction data in two passbands allows a crudethree-dimensional recovery of the dust structure, supporting thefront/back geometry derived from colors and extinction estimates. Thewhole feature contains on the order of 2×106Msolar in dust, implying about 3×108Msolar of gas and requiring a mass transfer rate averaging ~1Msolar yr-1, unless we are particularly unlucky inviewing angle. Curiously, this demonstrable case of mass transfer seemsto be independent of the occurrence of a Seyfert nucleus, since theSeyfert galaxy in this pair is the donor of the material. Likewise, therecipient shows no signs of recent star formation from incoming gas,although NGC 1410 has numerous luminous young star clusters andwidespread Hα emission.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 (AURA), Inc.,under NASA contract NAS 5-26555.
| Massive Star Clusters in Ongoing Galaxy Interactions: Clues to Cluster Formation
We present HST WFPC2 observations, supplemented by ground-based Hαdata, of the star-cluster populations in two pairs of interactinggalaxies selected for being in very different kinds of encounters seenat different stages. Dynamical information and n-body simulationsprovide the details of encounter geometry, mass ratio, and timing. InNGC 5752/4 we are seeing a weak encounter, well past closest approach,after about 2.5×108 yr. The large spiral NGC 5754 has anormal population of disk clusters, while the fainter companion NGC 5752exhibits a rich population of luminous clusters with a flatterluminosity function. The strong, ongoing encounter in NGC 6621/2, seenabout 1.0×108 yr past closest approach between roughlyequal-mass galaxies, has produced an extensive population of luminousclusters, particularly young and luminous in a small region between thetwo nuclei. This region is dynamically interesting, with such a strongperturbation in the velocity field that the rotation curve reversessign. From these results, in comparison with other strongly interactingsystems discussed in the literature, cluster formation requires athreshold level of perturbation, with stage of the interaction a lessimportant factor. The location of the most active star formation in NGC6621/2 draws attention to a possible role for the Toomre stabilitythreshold in shaping star formation in interacting galaxies. The richcluster populations in NGC 5752 and NGC 6621 show that direct contactbetween gas-rich galaxy disks is not a requirement to form luminousclusters and that they can be triggered by processes happening within asingle galaxy disk (albeit triggered by external perturbations).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 NAS 5-26555.
| Empirical Diagnostics of the Starburst-AGN Connection
We examine a representative sample of 35 Seyfert 2 nuclei. Previous workhas shown that nearly half (15) of these nuclei show the direct (butdifficult to detect) spectroscopic signature at optical/near-UVwavelengths of the hot massive stars that power circumnuclearstarbursts. In the present paper we examine a variety of more easilymeasured quantities for this sample, such as the equivalent widths ofstrong absorption features, continuum colors, emission line equivalentwidths, emission line ratios and profiles, far-IR luminosities, andnear-UV surface brightness. We compare the composite starburst+Seyfert 2nuclei to ``pure'' Seyfert 2 nuclei, Starburst galaxies, and normalgalactic nuclei. Our goals are to verify whether the easily measuredproperties of the composite nuclei are consistent with the expectedimpact of a starburst and to investigate alternative less demandingmethods to infer the presence of starbursts in Seyfert 2 nuclei,applicable to larger or more distant samples. We show that starbursts doindeed leave clear and easily quantifiable imprints on the near-UV tooptical continuum and emission line properties of Seyfert 2's. Compositestarburst+Seyfert 2 systems can be recognized by: (1) a strong``featureless continuum'' (FC), which dilutes the Ca II K line from oldstars in the host's bulge to an equivalent width WK<10Å (2) emission lines whose equivalent widths are intermediatebetween starburst galaxies and ``pure'' Seyfert 2's (3) relatively lowexcitation line ratios, which indicate that part of the gas ionizationin these Seyfert 2's (typically ~50% of Hβ) is due tophotoionization by OB stars; (4) large far-IR luminosities(>~1010 Lsolar) (5) high near-UV surfacebrightness (~103 Lsolar pc-2). Thesecharacteristics are all consistent with the expected impact ofcircumnuclear starbursts on the observed properties of Seyfert 2's.Furthermore, they offer alternative empirical diagnostics of thepresence of circumnuclear starbursts from a few easily measuredquantities.
| Ongoing Mass Transfer in the Interacting Galaxy Pair NGC 1409/10
I present two-band HST STIS imaging of ongoing mass transfer in theinteracting galaxy pair NGC 1409/10 (where NGC 1410 is the Seyfertgalaxy often listed as III Zw 55). Archival snapshot WFPC2 imaging fromthe survey by Malkan et al. showed a dust feature stretching between thegalaxies, apparently being captured by NGC 1409. The new images allowestimates of the mass being transferred and rate of transfer. Anabsorption lane typically 0.25" (100 pc) wide with a representativeoptical depth τ B = 0.2 cuts across the spiral structureof NGC 1410, crosses the 7-kpc projected space between the nuclei, wrapsin front of and, at the limits of detection, behind NGC 1409, andbecomes a denser (τ B = 0.4) polar ring around the coreof NGC 1409. Models for the light distribution in the two galaxies allowa crude three-dimensional recovery of the dust structure, supporting thefront/back geometry derived from colors and extinction estimates. Thewhole feature contains of order 5000 solar masses in dust, implyingabout 8 x 105 solar masses of gas. Incorporating theprojected velocity difference between nuclei for a timescale, thissuggests a very modest mass transfer rate averaging about 0.02 solarmasses per year unless we are particularly unlucky in viewing angle.Curiously, this demonstrable case of mass transfer seems to beindependent of the occurrence of a Seyfert nucleus, since the Seyfertgalaxy in this pair is the donor of the material. This work was supportby NASA through STScI grant GO-8147.01-97A.
| A Hubble Space Telescope Imaging Survey of Nearby Active Galactic Nuclei
We have obtained WFPC2 images of 256 of the nearest (z <= 0.035)Seyfert 1, Seyfert 2, and starburst galaxies. Our 500 s broadband(F606W) exposures reveal much fine-scale structure in the centers ofthese galaxies, including dust lanes and patches, bars, rings, wisps,and filaments, and tidal features such as warps and tails. Most of thisfine structure cannot be detected in ground-based images. We haveassigned qualitative classifications for these morphological featuresand a Hubble type for the inner region of each galaxy, and we have alsomeasured quantitative information such as 0."18 and 0."92 aperturemagnitudes, position angles, and ellipticities, where possible. There islittle direct evidence for unusually high rates of interaction in theSeyfert galaxies. Slightly less than 10% of all the galaxies show tidalfeatures or multiple nuclei. The incidence of inner starburst rings isabout 10% in both classes of Seyfert galaxies. In contrast, galaxieswith H II region emission-line spectra appear substantially moreirregular and clumpy because of their much higher rates of current starformation per unit of galactic mass. The presence of an unresolvedcentral continuum source in our Hubble Space Telescope images is avirtually perfect indicator of a Seyfert 1 nucleus as seen byground-based spectroscopy. Fifty-two percent of these Seyfert 1 pointsources are saturated in our images; we use their wings to estimatemagnitudes ranging from 15.8 to 18.5. The converse is not universallytrue, however, as over one-third of Seyferts with direct spectroscopicevidence for broad Balmer wings show no nuclear point source. These 34resolved Seyfert 1's have fainter nonstellar nuclei, which appear to bemore extinguished by dust absorption. Like the Seyfert 2's, they havecentral surface brightnesses consistent with those expected for thebulges of normal galaxies. The rates for the occurrences of bars inSeyfert 1's and 2's and non-Seyferts are the same. We found onesignificant morphological difference between the host galaxies ofSeyfert 1 and Seyfert 2 nuclei. The Seyfert 2 galaxies are significantlymore likely to show nuclear dust absorption, especially in lanes andpatches that are irregular or reach close to the nucleus. A few simpletests show that the difference cannot be explained by different averageredshifts or selection techniques. It is confirmed by our galaxymorphology classifications, which show that Seyfert 1 nuclei reside inearlier type galaxies than Seyfert 2 nuclei. If, as we believe, this isan intrinsic difference in host galaxy properties, it undermines one ofthe postulates of the strong unification hypothesis for Seyfertgalaxies, that they merely appear different because of the orientationof their central engine. The excess galactic dust we see in Seyfert 2'smay cause substantial absorption that obscures their hypothesized broademission line regions and central nonstellar continua. This galacticdust could produce much of the absorption in Seyfert 2 nuclei that hadinstead been attributed to a thick dusty accretion torus forming theouter part of the central engine.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| A Multiwavelength Catalog of Seyfert 2 Galaxies Observed in the 2--10 keV Energy Band
This paper is a catalog of Seyfert 2 galaxies observed in the 2-10 keVband (339 flux entries). In total, it contains data on 150 objects; for76 objects, a positive detection is reported, while for the remainingsources, 2 σ upper limits to the X-ray emission are given. Most ofthe data have been collected from the literature over a period startingfrom 1974 up to the middle of 1995. Accurate searches of literature anddatabases were performed for all objects, and frequently spectral fitswere reevaluated in order to make the data in the catalog uniform andcomplete. Some unpublished data are also included. For six objects,EXOSAT/ME date have been extracted from the satellite database andanalyzed; the 13 fluxes obtained have been added to the present catalog.The compilation of hard X-ray data has been complemented with data inthe soft (0.1-3 keV) X-ray band, as well as in ultraviolet (1450 A),optical (5500 A), infrared (3.5, 12, 25, 60, 100 micron), and radio (6cm) bands. Fluxes of the [O II] λ5007 and Hβ emission linesas well as the Balmer decrement Hα/Hβ, and axial ratio a/bare also given. The present database is meant to be a useful tool forthe study of the Seyfert 2 phenomenon in its various aspects.
| A Survey for H 2O Megamasers in Active Galactic Nuclei. I. Observations
We report an extensive search for 22 GHz H_2_O maser emission fromnearby active galaxies. Our sample includes all Seyfert and LINERgalaxies listed in the Huchra catalog or the Veron-Cetty & Veroncatalog with recessional velocities less than 7000 km s^-1^, and allSeyfert galaxies and LINERs in Huchra's catalog with m_b_ <= 14. Inaddition to these distance- and magnitude-limited samples, we have alsoobserved a number of active galaxies, including radio galaxies, athigher redshift; In all, some 354 galaxies have been surveyed. Ten newH_2_O megamaser sources have been detected, resulting in 16 galaxiesthat are currently known to contain H_2_O masers with isotropicluminosities greater than 20 L_sun_. Of the observed active galaxieswith cz < 7000 km s^-1^, 5.4% have detectable H_2_O megamaseremission. This fraction increases to 11% for those sources with cz <2000 km s^-1^. The newly discovered megamaser sources were monitored onsubsequent observing runs. The strength of the maser features varies forthese sources, as they do for Galactic masers. Three of the galaxieshave sufficient data to test for velocity changes of narrow masercomponents comparable in magnitude to those of the well-studied systemicfeatures in NGC 4258. The maser line in one of these galaxies-NGC2639-is found to have a systematic redward velocity drift of 6.6 +/- 0.4km s^-1^ yr^-1^. No systematic velocity drifts are found for the othertwo sources. We also report large apparent velocity changes in theunusual broad H_2_O emission feature in NGC 1052.
| Blue spectropolarimetry of Seyfert 2 galaxies. 1: Analysis and basic results
Spectropolarimetry in the 3200-6200 A range was obtained on 50 Seyert 2galaxies. After careful subtraction of a template galaxy, the fractionsof the total flux due to starlight Fg and to the featurelesscontinuum Fc were estimated. All of the Seyfert 2 galaxieshave a nonstellar component to their spectrum. Polarization is notcorrelted with Fc which argues against the hypothesis thatall Seyfert 2s have highly polarized featureless continua which areunseen because of dilution by starlight. The nine Seyfert 2s withspectropolarimetrically identified hidden broad-line regions (BLRs) havethe mean value of Fg = 0.30 considerably less than theaverage of 0.70 found for the larger sample. This suggests that thespectropolarimetric method of identifying hidden BLRs in Seyfert 2s ismost sensitive to objects in which the polarization is less contaminatedby a large fraction of starlight. The spectopolarimetric data indicatesa few additional objects, Mrk 266SW and Mrk 573, which may containhidden BLRs, but they require further study at H-alpha.
| Environments of Seyfert galaxies. I. Construction of the sample and selection effects.
In order to build a satisfactory picture of Seyferts in relation tonormal galaxies we have started a series of papers first establishingsome of their basic environmental properties, especially the differencein the number of close companions between Seyfert 1 and Seyfert 2galaxies. Here we report sample selections and discuss selection effectsinvolved for the samples of 104 Seyferts and 138 control galaxies. Theresults of the statistical analyses are presented by Laurikainen &Salo (1994, Paper II). The neighbouring galaxies are counted on thePalomar Sky Survey Plates to the limiting magnitude =~19m_pg_ within thecircles of 1.5Mpc in diameter (H_0_=100km/s/Mpc), large measuringcircles enabling good elimination of the background galaxies. Subsamplesare selected in order to test the methods by Dahari (1984) and byFuentes-Williams & Stocke (1988). Elimination of background galaxiesand problems related to comparison galaxy sample selection arediscussed. The most important problem in our control galaxy sampleselection is that the redshifts for most of the control galaxies areunknown. The size of this uncertainty is estimated by determining theredshifts by two ways: (1) by assuming that the selected comparisongalaxy has the same redshift as the nearby Seyfert and (2) byMonte-Carlo simulations for Holmberg (1975) galaxy size distribution inspace, taking into account the Malmquist bias. The mean redshifts of thecomparison sample are estimated with these methods to be 0.028 and0.029, respectively, compared with 0.026 for the Seyfert sample.Distribution of Seyferts in Zwicky's clusters is also addressed, andcompared with previous studies. Taking into account optical projections,about 3/4 of the Seyferts are found to be field galaxies. Galaxies inclusters lie preferentially at the cluster borders.
| An optical catalog of extragalactic emission-line objects similar to quasi-stellar objects
A catalog of 935 galaxies which have optical properties similar to thoseof QSOs is given. A subsidiary table of cross-identifications enablesthe reader to relate the name of a given object to its coordinate name.Most of the objects appear to be nonstellar. The majority, more than700, have redshifts z = 0.2 or less, and have mostly been classified asSeyfert galaxies, N systems, or radio galaxies. The Hubble diagram forall of the objects with z = 0.2 or less is shown. The redshiftdistribution peaks at z = 0.025, but there are about 200 powerful radiogalaxies in the extended tail of the distribution which have z greaterthan 0.2. There is a separate and distinct peak in the redshiftdistribution at z = 0.06.
| Star formation in a sample of interacting galaxies
The star formation properties are analyzed for a sample of interactinggalaxies based on long-slit optical spectroscopy observations, and theresults are reported. A high frequency of LINERs is detected among thesample galaxies, many of which show only low-level activity and are notassociated with high infrared flux LINERs. Their global star-formationrates are higher than for field galaxies in most of the systems. Thestar-formation activity is mainly concentrated toward the central partsof the strongly interacting galaxies. Extended emission can appear ingalaxies of very spectral type when the activity level is very high, butit is not a general feature. The star formation in a galaxy in everygeneration of its 'ecologic cycle' of molecular cloud and star formationis found to be essentially produced with the same spatial distribution.
| Observations of binary galaxies at a frequency of 102 MHz
A total of 93 double galaxies from the Karachentsev list was observedwith the large phased array at the Lebedev Physical Institute at 102MHz. The interplanetary oscillation method was used. Two of the galaxieswere found to contain scintillating components with angular dimensionsof less than 1 arcsec and flux densities of more than 1 Jy. Theobservations of double galaxies at low radio frequencies indicate thatgalaxies in pairs are more active than single galaxies.
| A statistical study of properties of Seyfert and starburst galaxies
Spectral and morphological data for 282 Seyfert and emission-linegalaxies spanning radio to X-ray wavelengths are compiled. The datainclude a large number of optical emission-line measurements which havenot been reported previously. These data are intended to provide aconvenient summary of the relevant properties of these galaxies, as wellas a data base to search for correlations among the various parametersin order to obtain a better understanding of the active galaxyphenomenon. The paper presents the data and analyzes the distributionsof various properties of Seyfert 1 and Seyfert 2 galaxies and starburstgalaxies. It is found that Seyferts 2s have a higher 60 micron/forbiddenO III 5007 A flux ratio than Seyfert 1s. This result, combined with thefact that Seyfert 2s are more heavily reddened, indicate that they havea higher dust content. It is also found that starburst nuclei arecomparable to Seyfert 2s in far-infrared and 20 cm luminosities,although their optical spectra are markedly different.
| Two interacting Seyfert 2 galaxies - VV 343 and III ZW 55
Spectroscopic results are presented for the nonisolated Seyfert 2galaxies NGC 7674 and III Zw 55 and their respective companions. Thevalues of the redshifts confirm that both active galaxies are members ofphysical groups. Signs of the presence of dynamical instabilities arefound in both of the Seyfert galaxies. The extended emission in NGC 7674and part of the far-IR fluxes of NGC 1410 are interpreted as beingproduced by hot, newly produced stars. Because of the significantdifferences in the level of activity in the two Seyfert objects, it isargued that even if gravitational interaction can trigger nuclearactivity, the form in which it manifests itself largely depends on theparticular properties of each object.
| 10.7 GHz observations of Markarian/Seyfert galaxies
In this paper, 10.7 GHz observations of 55 Seyfert galaxies, mostly fromMarkarian lists are presented. Ten galaxies were detected withcertainty, and probably five more. The results are briefly discussed.Inasmuch as the limited sample allows, it is concluded that thedetection statistics are similar for both Seyfert 1 and Seyfert 2galaxies. Seyfert 1 galaxies tend to have steeper radio spectra andlower radio/far-infrared flux-density ratios than Seyfert 2 galaxies.
| Double galaxy investigations. I - Observations
Redshift information from 240 A/mm spectrograms is presented for 370double arcsec galaxy systems from the Karachentsev (1972) catalog,including all pairs in that catalog with separation less than 80 arcsec.An extensive error discussion utilizing internal and external (21 cm)comparisons provides calibration of systematic error and determines theuncertainty for a typical high weight optical redshift to be plus orminus 65 km/sec. Internal differential redshifts within single spectrausing common lines achieve accuracies of 18-30 km/sec, depending uponseparation, and are available for about 200 pairs. Extensive informationon emission and other properties is also provided.
| Atlas of interacting galaxies, Part. II and the concept of fragmentation of galaxies.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...28....1V&db_key=AST
| Radial velocities of double galaxies
Spectral observations of 92 galaxies in isolated pairs have been carriedout. In 52 cases radial velocities were measured. The mean value of theorbital mass-to-luminosity ratio for 18 pairs is (16.2 plus or minus10.0) times the solar value.
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