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HI content in galaxies in loose groups
Gas deficiency in cluster spirals is well known and ram-pressurestripping is considered the main gas removal mechanism. In some compactgroups too gas deficiency is reported. However, gas deficiency in loosegroups is not yet well established. Lower dispersion of the membervelocities and the lower density of the intragroup medium in small loosegroups favour tidal stripping as the main gas removal process in them.Recent releases of data from the HI Parkes All-Sky Survey (HIPASS) andcatalogues of nearby loose groups with associated diffuse X-ray emissionhave allowed us to test this notion. In this paper, we address thefollowing questions: (i) do galaxies in groups with diffuse X-rayemission statistically have lower gas content compared to the ones ingroups without diffuse X-ray emission? (ii) does HI deficiency vary withthe X-ray luminosity, LX, of the loose group in a systematicway? We find that (i) galaxies in groups with diffuse X-ray emission, onaverage, are HI deficient, and have lost more gas compared to those ingroups without X-ray emission; the latter are found not to havesignificant HI deficiency; (ii) no systematic dependence of the HIdeficiency with LX is found. Ram-pressure-assisted tidalstripping and evaporation by thermal conduction are the two possiblemechanisms to account for this excess gas loss.
| The Two-dimensional XMM-Newton Group Survey: z < 0.012 Groups
We present the results of the two-dimensional XMM-Newton Group Survey(2dXGS), an archival study of nearby galaxy groups. In this paper weconsider 11 nearby systems (z<0.012) in Mulchaey et al., which span abroad range in X-ray luminosity from 1040 to 1043ergs s-1. We measure the iron abundance and temperaturedistribution in these systems and derive pressure and entropy maps. Wefind statistically significant evidence for structure in the entropy andpressure of the gas component of seven groups on the 10%-20% level. TheXMM-Newton data for the three groups with best statistics also suggestpatchy metallicity distributions within the central 20-50 kpc of thebrightest group galaxy, probed with 2-10 kpc resolution. This providesinsights into the processes associated with thermalization of thestellar mass loss. Analysis of the global properties of the groupsreveals a subclass of X-ray-faint groups, which are characterized byboth higher entropy and lower pressure. We suggest that the mergerhistory of the central elliptical is responsible for both the source andthe observed thermodynamical properties of the hot gas of theX-ray-faint groups.
| Spitzer IRS Spectra of a Large Sample of Seyfert Galaxies: A Variety of Infrared Spectral Energy Distributions in the Local Active Galactic Nucleus Population
We are conducting a large observing program with the Spitzer SpaceTelescope to determine the mid- to far-IR spectral energy distributionsof a well-defined sample of 87 nearby, 12 μm-selected Seyfertgalaxies. In this paper we present the results of Spitzer IRSlow-resolution spectroscopy of a statistically representative subsampleof 51 of the galaxies (59%), with an analysis of the continuum shapesand a comparison of the Seyfert types. We find that the spectra clearlydivide into groups based on their continuum shapes and spectralfeatures. The largest group (47% of the sample of 51) shows a very redcontinuum suggestive of cool dust and strong emission featuresattributed to polycyclic aromatic hydrocarbons. Sixteen objects (31%)have a power-law continuum with spectral indices of α5-20μm=-2.3 to -0.9 that flatten to α20-35μm=-1.1 to 0.0 at ~20 μm. Clear silicate emission featuresat 10 and 18 μm are found in two of these objects (Mrk 6 and Mrk335). A further 16% of the sample show power-law continua withunchanging slopes of α5-35 μm=-1.7 to -1.1. Twoobjects are dominated by a broad silicate absorption feature. One objectin the sample shows an unusual spectrum dominated by emission features,which is unlike any of the other spectra. Some spectral features areclearly related to a starburst contribution to the IR spectrum, whilethe mechanisms producing observed power-law continuum shapes, attributedto an active galactic nucleus (AGN) component, may be dust or nonthermalemission. The IR spectral types appear to be related to the Seyferttypes. Principal component analysis results suggest that the relativecontribution of starburst emission may be the dominant cause of variancein the observed spectra. The derived starburst component of eachspectrum, however, contributes <40% of the total flux density. Wecompare the IR emission with the optically thin radio emissionassociated with the AGN and find that Seyfert 1 galaxies have higherratios of IR to radio emission than Seyfert 2 galaxies, as predicted bythe unified model if the torus is optically thick in the mid-IR.However, smooth-density torus models predict a much larger differencebetween Seyfert types 1 and 2 than the factor of 2 difference observedin our sample; the observed factor of ~2 difference between the type 1and type 2 galaxies in their IR-to-radio ratios above 15 μm requiresthe standard smooth-density torus models to be optically thin at thesewavelengths. However, the resulting low torus opacity requires that thehigh observed columns detected in X-ray absorption be produced in gaswith a very low dust-to-gas ratio (perhaps within the dust sublimationregion). On the other hand, our observations may be consistent withclumpy torus models containing a steep radial distribution of opticallythick dense clumps. The selection of our sample at 12 μm, where thetorus may be optically thick, implies that there may beorientation-dependent biases in the sample; however, we do not find thatthe sample is biased toward Seyfert 2 galaxies with more luminouscentral engines, as would be expected. We find that the Seyfert 2galaxies typically show stronger starburst contributions than theSeyfert 1 galaxies in the sample, contrary to what is expected based onthe unified scheme for AGNs. This may be due to the selection effectthat only those Seyfert 2 galaxies with strong starburst contributionshad high enough integrated 12 μm flux densities to fall above theflux limit of the sample.
| Toward a clean sample of ultra-luminous X-ray sources
Context: .Observational follow-up programmes for the characterization ofultra-luminous X-ray sources (ULXs) require the construction of cleansamples of such sources in which the contamination byforeground/background sources is minimum. Aims: .We calculate thedegree of foreground/background contaminants among the ULX samplecandidates in a published catalogue and compare these computations withavailable spectroscopic identifications. Methods: .We usestatistics based on known densities of X-ray sources and AGN/QSOsselected in the optical. The analysis is done individually for eachparent galaxy. The existing identifications of the optical counterpartsare compiled from the literature. Results: .More than a half ofthe ULXs, within twice the distance of the major axis of the 25mag/arcsec2 isophote from RC3 nearby galaxies and with X-rayluminosities L_X[ 2-10 keV] ≥ 1039 erg/s, are expected tobe high redshift background QSOs. A list of 25 objects (clean sample)confirmed to be real ULXs or to have a low probability of beingcontaminant foreground/background objects is provided.
| The K-band properties of Seyfert 2 galaxies
Aims. It is well known that the [O iii]λ5007 emission line andhard X-ray (2-10 keV) luminosities are good indicators of AGN activitiesand that the near and mid-infrared emission of AGN originates fromre-radiation of dusty clouds heated by the UV/optical radiation from theaccretion disk. In this paper we present a study of the near-infraredK-band (2.2 μm) properties for a sample of 65 Seyfert 2 galaxies. Methods: .By using the AGN/Bulge/Disk decomposition technique, weanalyzed the 2MASS K_S-band images for Seyfert 2 galaxies in order toderive the K_S-band magnitudes for the central engine, bulge, and diskcomponents. Results: .We find that the K_S-band magnitudes of thecentral AGN component in Seyfert 2 galaxies are tightly correlated withthe [O iii]λ5007 and the hard X-ray luminosities, which suggeststhat the AGN K-band emission is also an excellent indicator of thenuclear activities at least for Seyfert 2 galaxies. We also confirm thegood relation between the central black hole masses and bulge's K-bandmagnitudes for Seyfert 2s.
| An atlas of calcium triplet spectra of active galaxies
We present a spectroscopic atlas of active galactic nuclei covering theregion around the λλ8498, 8542, 8662 calcium triplet(CaT). The sample comprises 78 objects, divided into 43 Seyfert 2s, 26Seyfert 1s, three starburst and six normal galaxies. The spectra pertainto the inner ~300 pc in radius, and thus sample the central kinematicsand stellar populations of active galaxies. The data are used to measurestellar velocity dispersions (σ*) with bothcross-correlation and direct fitting methods. These measurements arefound to be in good agreement with each other and with those in previousstudies for objects in common. The CaT equivalent width is alsomeasured. We find average values and sample dispersions ofWCaT of 4.6 +/- 2.0, 7.0 +/- 1.0 and 7.7 +/- 1.0 Å forSeyfert 1s, Seyfert 2s and normal galaxies, respectively. We furtherpresent an atlas of [SIII]λ9069 emission-line profiles for asubset of 40 galaxies. These data are analysed in a companion paperwhich addresses the connection between stellar and narrow-line regionkinematics, the behaviour of the CaT equivalent width as a function ofσ*, activity type and stellar population properties.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| A sample of X-ray emitting normal galaxies from the BMW-HRI Catalogue
We obtained a sample of 143 normal galaxies with X-ray luminosity in therange 1038{-}1043 erg s-1 from thecross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI)Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We findthat the average X-ray properties of this sample are in good agreementwith those of other samples of galaxies in the literature. We selected acomplete flux limited serendipitous sample of 32 galaxies from which wederived the log N-log S distribution of normal galaxies in the fluxrange 1.1{-} 110 × 10-14 erg cm-2s-1. The resulting distribution is consistent with theEuclidean -1.5 slope. Comparisons with other samples, such as theExtended Medium Sensitivity Survey, the ROSAT All Sky Survey, theXMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate thatthe log N -log S distribution of normal galaxies is consistent with aEuclidean slope over a flux range of about 6 decades.
| Intergalactic neutral hydrogen gas in the Grus quartet of galaxies
Australia Telescope Compact Array multi-configuration mosaicing of theGrus quartet of galaxies reveals the presence of spectacular tidalstructures. 2.1×109 Mȯ of neutralatomic hydrogen (H I) gas, i.e. 11% of all H I in the group, are foundto be dragged from NGC 7582 into intergalactic space. About1.34×109 Mȯ of H I gas are contained ina tidal tail emanating from the north-western disk of NGC 7582, with aprojected length of about 85 kpc and width of up to 32 kpc and arelative velocity with respect to the centre of NGC 7582 of 130-140 kms-1. 7.7×108 Mȯ of H Ireside in an intergalactic H I cloud 48 kpc West of NGC 7582, whichmight originate from the disk of NGC 7582 as well and has no opticalcounterpart in a red Digital Sky Survey (DSS) image. These observationsprove that tidal stripping is occurring in the Grus quartet and thattidal features in compact groups can be potentially importantcontributors of metal-enriched matter to the intergalactic medium. Thetidal features around NGC 7582 cover an area of about 2000kpc2, almost doubling the group's cross-section forLyman-α absorption of light from background sources compared tothe optical extent of the member galaxies.
| A catalogue of ultraluminous X-ray sources in external galaxies
We present a catalogue of ultraluminous X-ray sources (ULXs) in externalgalaxies. The aim of this catalogue is to provide easy access to theproperties of ULXs, their possible counterparts at other wavelengths(optical, IR, and radio), and their host galaxies. The cataloguecontains 229 ULXs reported in the literature until April 2004. Most ULXsare stellar-mass-black hole X-ray binaries, but it is not excluded thatsome ULXs could be intermediate-mass black holes. A small fraction ofthe candidate ULXs may be background Active Galactic Nuclei (AGN) andSupernova Remnants (SNRs). ULXs with luminosity above 1040ergs s-1 are found in both starburst galaxies and in thehalos of early-type galaxies.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/1125
| The star formation history of Seyfert 2 nuclei
We present a study of the stellar populations in the central ~200 pc ofa large and homogeneous sample comprising 79 nearby galaxies, most ofwhich are Seyfert 2s. The star formation history of these nuclei isreconstructed by means of state-of-the-art population synthesismodelling of their spectra in the 3500-5200 Åinterval. Aquasar-like featureless continuum (FC) is added to the models to accountfor possible scattered light from a hidden active galactic nucleus(AGN).We find the following. (1) The star formation history of Seyfert 2nuclei is remarkably heterogeneous: young starbursts, intermediate-ageand old stellar populations all appear in significant and widely varyingproportions. (2) A significant fraction of the nuclei show a strong FCcomponent, but this FC is not always an indication of a hidden AGN: itcan also betray the presence of a young, dusty starburst. (3) We detectweak broad Hβ emission in several Seyfert 2s after cleaning theobserved spectrum by subtracting the synthesis model. These are mostlikely the weak scattered lines from the hidden broad-line regionenvisaged in the unified model, given that in most of these casesindependent spectropolarimetry data find a hidden Seyfert 1. (4) The FCstrengths obtained by the spectral decomposition are substantiallylarger for the Seyfert 2s which present evidence of broad lines,implying that the scattered non-stellar continuum is also detected. (5)There is no correlation between the star formation in the nucleus andeither the central or overall morphology of the parent galaxies.
| Stellar populations and dust extinction in non-active and Seyfert spiral galaxies
Metallicity and age gradients of the stellar populations and dustextinction are studied for a sample of 32 non-active, seven type 1Seyfert (S1) and 17 type 2 Seyfert (S2) spiral galaxies. The samplegalaxies cover the whole range from face-on to edge-on view, and thevariation of the optical and near-infrared colour gradients in the discas a function of the inclination angle is investigated in order toseparate colour changes caused by population gradients from those due todust effects.The measurements show that the observed colour gradients in the discs ofthe non-active galaxies are significantly larger than those found forthe S1 and S2 galaxies. In the near-infrared wavelengths, however, thesedifferences disappear, and the colour gradients are the same for allthree galaxy types. No systematic differences are found between thecolour gradients of the discs of the S1 galaxies and those of the S2galaxies.The data are compared to model images of dusty galaxies with a varietyof age and metallicity gradients in the disc. The radial variations ofthe optical and near-infrared colours of the model galaxies arecalculated from the radial changes of the ages and the metallicities ofthe stars, using broad-band colours of a single stellar population. Thestellar content at a given position in the disc is determined by theaverage age, the metallicity and the star formation history.For the non-active galaxies, the observed colour gradients arerepresented best by a model with a metallicity gradient, with the innerregions of the stellar disc being more metal-rich than the outerregions. However, the presence of an age gradient, with the innerregions of the stellar disc being older than the outer regions, cannotbe ruled out. For the S1 and S2 galaxies, the comparison between dataand models indicates that the age and metallicity gradients in thestellar disc are small. As far as the internal dust extinction isconcerned, the comparison between data and models indicates that boththe non-active and the S2 galaxies show significant dust extinction, butthey are not optically thick.
| Spectropolarimetry of Compton-thin Seyfert 2 galaxies
We present new spectropolarimetry of a sample of nearby Compton-thinSeyfert 2 galaxies (i.e. those with NH < 1023cm-2). We show that the detection rate of scattered broadHα in this sample is considerably higher than in Seyfert 2galaxies as a whole. Our results also show that in this low obscurationset it is possible to find scattered broad Hα even when the globalproperties of the galaxy are largely dominated by the host galaxy andnot the active galactic nucleus. These results argue against theexistence of a population of `pure' Seyfert 2 galaxies.
| An IRAS High Resolution Image Restoration (HIRES) Atlas of All Interacting Galaxies in the IRAS Revised Bright Galaxy Sample
The importance of far-infrared observations for our understanding ofextreme activity in interacting and merging galaxies has beenillustrated by many studies. Even though two decades have passed sinceits launch, the most complete all-sky survey to date from which far-IRselected galaxy samples can be chosen is still that of the InfraredAstronomical Satellite (IRAS). However, the spatial resolution of theIRAS all-sky survey is insufficient to resolve the emission fromindividual galaxies in most interacting galaxy pairs, and hence previousstudies of their far-IR properties have had to concentrate either onglobal system properties or on the properties of very widely separatedand weakly interacting pairs. Using the HIRES image reconstructiontechnique, it is possible to achieve a spatial resolution ranging from30" to 1.5m (depending on wavelength and detector coverage), whichis a fourfold improvement over the normal resolution of IRAS. This issufficient to resolve the far-IR emission from the individual galaxiesin many interacting systems detected by IRAS, which is very importantfor meaningful comparisons with single, isolated galaxies. We presenthigh-resolution 12, 25, 60, and 100 μm images of 106 interactinggalaxy systems contained in the IRAS Revised Bright Galaxy Sample (RBGS,Sanders et al.), a complete sample of all galaxies having a 60 μmflux density greater than 5.24 Jy. These systems were selected to haveat least two distinguishable galaxies separated by less than threeaverage galactic diameters, and thus we have excluded very widelyseparated systems and very advanced mergers. Additionally, some systemshave been included that are more than three galactic diameters apart,yet have separations less than 4' and are thus likely to suffer fromconfusion in the RBGS. The new complete survey has the same propertiesas the prototype survey of Surace et al. We find no increased tendencyfor infrared-bright galaxies to be associated with other infrared-brightgalaxies among the widely separated pairs studied here. We find smallenhancements in far-IR activity in multiple galaxy systems relative toRBGS noninteracting galaxies with the same blue luminosity distribution.We also find no differences in infrared activity (as measured byinfrared color and luminosity) between late- and early-type spiralgalaxies.
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| Asteroid database
The development and significance of asteroid database are reviewed inthis paper. Some of online database of asteroid are presented andcompared briefly, including asteroid orbital elements database, asteroidphotometric database, asteroid infrared database, near earth asteroiddatabase and asteroid database. Ephemeris service based on asteroiddatabase is mentioned. The trend of development of asteroid database hasalso been discussed.
| Chandra Observations of NGC 4698: A Seyfert 2 Galaxy with No Absorption
We present Chandra ACIS-S observations of the enigmatic Seyfert 2 galaxyNGC 4698. This object, together with several other bona fide Seyfert 2galaxies, shows no absorption in the low spatial resolution ASCA data,in contrast to the standard unification models. Our Chandra observationsof NGC 4698 probe directly the nucleus, allowing us to check whethernearby sources contaminate the ASCA spectrum. Indeed, the Chandraobservations show that the ASCA spectrum is dominated by two nearbyAGNs. The X-ray flux of NGC 4698 is dominated by a nuclear source withluminosity L0.3-8keV~1039 ergs s-1,coincident with the radio nucleus. Its spectrum is well represented by apower law, Γ~2.2, obscured by a small column density of5×1020 cm-2, suggesting that NGC 4698 is anatypical Seyfert galaxy. On the basis of its low luminosity, we theninterpret NGC 4698 as a Seyfert galaxy that lacks a broad-line region.
| The Lack of Broad-Line Regions in Low Accretion Rate Active Galactic Nuclei as Evidence of Their Origin in the Accretion Disk
In this Letter, we present evidence suggesting that the absence orpresence of hidden broad-line regions (HBLRs) in Seyfert 2 galaxies isregulated by the rate at which matter accretes onto a centralsupermassive black hole, in units of the Eddington rate. Evidence isbased on data from a subsample of type 2 active galactic nucleiextracted from the Tran spectropolarimetric sample and made up of allthose sources that also have good-quality X-ray spectra available andfor which a bulge luminosity can be estimated. We use the intrinsic(i.e., unabsorbed) X-ray luminosities of these sources and their blackhole masses (estimated by using the well-known relationship betweennuclear mass and bulge luminosity in galaxies) to derive the nuclearaccretion rate in Eddington units. We find that virtually all HBLRsources have accretion rates larger than a threshold value ofmthres~=10-3 (in Eddington units), while non-HBLRsources lie at m<~mthres. These data nicely fitpredictions from a model proposed by Nicastro in which the broad-lineregions (BLRs) are formed by accretion disk instabilities occurring inproximity of the critical radius at which the disk changes from gaspressure dominated to radiation pressure dominated. This radiusdiminishes with decreasing m for low enough accretion rates (andtherefore luminosities), the critical radius becomes smaller than theinnermost stable orbit and BLRs cannot form.
| The Unified Model and Evolution of Active Galaxies: Implications from a Spectropolarimetric Study
We extend the analysis presented in Paper I of a spectropolarimetricsurvey of the CfA and 12 μm samples of Seyfert 2 galaxies (S2s). Weconfirm that polarized (hidden) broad-line region (HBLR) S2s tend tohave hotter circumnuclear dust temperatures, show mid-IR spectra morecharacteristic of Seyfert 1 galaxies (S1s), and are intrinsically moreluminous than non-HBLR S2s. The levels of obscuration and circumnuclearstar formation, however, appear to be similar between HBLR and non-HBLRS2 galaxies, based on an examination of various observationalindicators. HBLR S2s, on average, share many similar large-scale,presumably isotropic, characteristics with S1s, as would be expected ifthe unified model is correct, while non-HBLR S2s generally do not. Theactive nuclear engines of non-HBLR S2s, then, appear to be truly weakerthan HBLR S2s, which in turn are fully consistent with being S1s viewedfrom another direction. There is also evidence that the fraction ofdetected HBLRs increases with the radio power of the active galacticnucleus. Thus, all S2 galaxies may not be intrinsically similar innature, and we speculate that evolutionary processes may be at work.
| 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.
| The Role of Interactions in the Evolution of Highly Star-forming Early-Type (Sa-Sab) Spiral Galaxies
We present a search for the signatures of galaxy-galaxy interactions inthe neutral gas of early-type spirals. New neutral hydrogen observationsfor four highly star-forming early-type spirals are presented here,along with H I data for three additional galaxies from other sources. HI maps of six of seven galaxies reveal unambiguous signs of a recentencounter, via tidal tails and H I bridges. Most of these galaxiesappear undisturbed in the optical, and these interactions probably wouldhave gone unnoticed without H I mapping. Such high rates of interactionsuggest that galactic encounters may play an important role in theevolution of early-type spiral galaxies.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and 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/405/5
| Comparisons of Infrared Colors and Emission-line Intensities between Two types of Seyfert 2 Galaxies
We study the relation between the infrared colors, [OIII] emissionlines, gaseous absorbing column density (NH),and thedetectability of the polarized (hidden) broad-line region (HBLR) in alarge sample of 75 Seyfert 2 galaxies (Sy2s). From the indicators ofstar-formation activity, f60/f100 andLFIR/LB, we find some evidence that the Sy2swithout HBLR show higher star-formation activities than those with HBLR,in agreement with previous prediction. Also, we confirm that the HBLRSy2s tend to have a larger luminosity ratio of the core to the hostgalaxy, suggesting that the HBLR Sy2s display more powerful AGNactivity. However, the level of obscuration found in previous papers isnearly indistinguishable between the two types of Sy2s. The resultssupport the statement that the non-HBLR Sy2s, with a weaker corecomponent and a stronger star-formation activity component, areintrinsically different from the HBLR Sy2s, which are Sy1 systems with ahidden powerful AGN core and a low star-formation activity. Theindications are that the non-HBLR Sy2s might be at an earlierevolutionary phase than the HBLR Sy2s.
| A Catalog of Candidate Intermediate-Luminosity X-Ray Objects
ROSAT, and now Chandra, X-ray images allow studies of extranuclear X-raypoint sources in galaxies other than our own. X-ray observations ofnormal galaxies with ROSAT and Chandra have revealed that off-nuclear,compact, intermediate-luminosity(LX[2-10keV]>=1039.0 ergs s-1) X-rayobjects (IXOs, a.k.a. ULXs [ultraluminous X-ray sources]) are quitecommon. Here we present a catalog and finding charts for 87 IXOs in 54galaxies, derived from all of the ROSAT HRI imaging data for galaxieswith cz<=5000 km s-1 from the Third Reference Catalog ofBright Galaxies. We have defined the cutoff LX for IXOs sothat it is well above the Eddington luminosity of a 1.4Msolar black hole (1038.3 ergs s-1), soas not to confuse IXOs with ``normal'' black hole X-ray binaries. Thiscatalog is intended to provide a baseline for follow-up work withChandra and XMM-Newton, and with space- and ground-based survey work atwavelengths other than X-ray. We demonstrate that elliptical galaxieswith IXOs have a larger number of IXOs per galaxy than nonellipticalgalaxies with IXOs and note that they are not likely to be merelyhigh-mass X-ray binaries with beamed X-ray emission, as may be the casefor IXOs in starburst galaxies. Approximately half of the IXOs withmultiple observations show X-ray variability, and many (19) of the IXOshave faint optical counterparts in DSS optical B-band images. Follow-upobservations of these objects should be helpful in identifying theirnature.
| Seyfert 2 Galaxies with Spectropolarimetric Observations
We present a compilation of radio, infrared, optical, and hard X-ray(2-10 keV) data for a sample of 90 Seyfert 2 galaxies (Sy2s) withspectropolarimetric observations (41 Sy2s with detection of polarizedbroad lines [PBLs] and 49 without PBLs). Compared to Sy2s without PBLs,Sy2s with PBLs tend to be earlier type spirals and show warmermidinfrared color and significant excess of emissions (including thehard X-ray [2-10 keV], [O III] λ5007, infrared [25 μm], andradio). Our analyses indicate that the majority of Sy2s without PBLs arethose sources having less powerful active galactic nucleus (AGN)activities, most likely caused by a low accretion rate. It implies thatthe detectability of the polarized broad emission lines in Sy2s maydepend on their central AGN activities in most cases. Based on theavailable data, we find no compelling evidence for the presence of twotypes of Sy2s; one of which has been proposed to be intrinsicallydifferent from Sy2s claimed in the unification model.
| The Far-Infrared Energy Distributions of Seyfert and Starburst Galaxies in the Local Universe: Infrared Space Observatory Photometry of the 12 Micron Active Galaxy Sample
New far-infrared photometry with ISOPHOT aboard the Infrared SpaceObservatory (ISO) is presented for 58 galaxies with homogeneouspublished data for another 32 galaxies, all belonging to the 12 μmgalaxy sample-in total, 29 Seyfert 1 galaxies, 35 Seyfert 2 galaxies,and 12 starburst galaxies, or about half of the 12 μm active galaxysample, plus 14 normal galaxies for comparison. ISO and InfraredAstronomical Satellite (IRAS) data are used to define color-colordiagrams and spectral energy distributions (SEDs). Thermal dust emissionat two temperatures (one cold at 15-30 K and one warm at 50-70 K) canfit the 60-200 μm SED, with a dust emissivity law proportional to theinverse square of the wavelength. Seyfert 1 galaxies and Seyfert 2galaxies are indistinguishable longward of 100 μm, while, as alreadyseen by IRAS, the former have flatter SEDs shortward of 60 μm. A mildanticorrelation is found between the [200-100] color and the ``60 μmexcess.'' We infer that this is due to the fact that galaxies with astrong starburst component and thus a strong 60 μm flux have asteeper far-infrared turnover. In non-Seyfert galaxies, increasing theluminosity corresponds to increasing the star formation rate, whichenhances the 25 and 60 μm emission. This shifts the peak emissionfrom around 150 μm in the most quiescent spirals to shorter than 60μm in the strongest starburst galaxies. To quantify these trendsfurther, we identified with the IRAS colors three idealized infraredSEDs: pure quiescent disk emission, pure starburst emission, and pureSeyfert nucleus emission. Even between 100 and 200 μm, the quiescentdisk emission remains much cooler than the starburst component. Seyfertgalaxies have 100-200 μm SEDs ranging from pure disks to purestarbursts, with no apparent contribution from their active nuclei atthose wavelengths. Based on observations with ISO, an ESA project withinstruments funded by ESA Member States (especially the PI countries:France, Germany, the Netherlands, and the United Kingdom) with theparticipation of ISAS and NASA.
| Chandra Observations of Markarian 273: Unveiling the Central Active Galactic Nucleus and the Extended Hot Gas Halo
We report X-ray observations of the field containing the ultraluminousIRAS galaxy Mrk 273. The data were obtained using the Advanced CCDImaging Spectrometer S3 instrument on board Chandra. The high-resolutionX-ray image for the first time reveals a compact hard X-ray nucleus inMrk 273. Its position is coincident with the northern nucleus identifiedin the optical, infrared, and radio and in molecular CO maps. Its X-rayenergy distribution is well described by a heavily obscured activegalactic nucleus (AGN) spectrum with an absorbed power law plus a narrowFe Kα emission line at 6.4 keV. The neutral hydrogen columndensity is about 4×1023 cm-2, implying anabsorption-corrected X-ray luminosity (0.1-10 keV) for the nucleus ofLX~6.5×1043 ergs s-1 forH0=50 km s-1 Mpc-1. The X-rayproperties therefore firmly establish the northern nucleus of Mrk 273 asa Seyfert 2 AGN. There are also bright soft X-ray clumps and diffusesoft X-ray emissions surrounding the central hard X-ray nucleus withinthe 10" of the nuclear region. Its spectrum can be fitted by a MEKALthermal model with a temperature of about 0.8 keV and high metallicity(Z~1.5 Zsolar) plus emission lines from α elements andions. We find that a soft X-ray clump, about 4" (projected separation ofabout 4 kpc) southwest of the northern hard X-ray nucleus, is coincidentwith a nebula with strong [O III] λ5007 emissions. Furtheroutside the central region, the Chandra observations reveal a veryextended hot halo in Mrk 273. The X-ray halo encompasses the entireoptical tidal tail and plume, with a projected diameter of about108×68 kpc. The total soft X-ray luminosity (0.1-2.4 keV) of thehot halo is LX~1.9×1041 ergs s-1,in the range of the soft X-ray luminosity of bright elliptical galaxies.The temperature of the hot gas is about 0.62 keV with a low metallicity(Z~0.1 Zsolar). We discuss the nature of the AGN in Mrk 273and the implications of our results on the origin of X-ray halos inelliptical galaxies. We also discuss the properties of Mrk 273x, abackground AGN at redshift z=0.46 in the Mrk 273 field. The AGN has anX-ray luminosity of LX~2.43×1044 ergss-1 in the 0.5-10 keV band. Its X-ray properties resemblethose of Seyfert 1 galaxies, while its optical properties are similar toSeyfert 2 galaxies. Such mixed classifications in the optical and X-raymay be a challenge for the unification scheme of AGNs.
| Unabsorbed Seyfert 2 galaxies
We present a sample of 17 type 2 Seyfert galaxies which have an X-raycolumn density lower than 1022 cm-2. The Comptonthin nature of these sources is strongly suggested by isotropicindicators. We estimate the fraction of these sources to be in the rangeof 10%-30% of the population of type 2 Seyfert galaxies. Furthermore,this fraction appears to increase progressively at lower luminosities.The simple formulation of the Unified Model for Seyfert galaxies is notapplicable in such sources since the pc-scale molecular torus is notlikely to be responsible for the low column density observed; insteadthe absorption observed is likely to originate at larger scales.According to this hypothesis, in these objects the broad line regionsare covered by some dusty obscuring material. In particular, this couldoccur in objects with dust lanes, patches or HII regions. However, wecannot rule out that in the lowest luminosity sources the BLR is weak,absent or has faded away. This last scenario is consistent with thepredictions of some recent theoretical models for low luminosity AGNs.
| Local velocity field from sosie galaxies. I. The Peebles' model
Pratton et al. (1997) showed that the velocity field around clusterscould generate an apparent distortion that appears as tangentialstructures or radial filaments. In the present paper we determine theparameters of the Peebles' model (1976) describing infall of galaxiesonto clusters with the aim of testing quantitatively the amplitude ofthis distortion. The distances are determined from the concept of sosiegalaxies (Paturel 1984) using 21 calibrators for which the distanceswere recently calculated from two independent Cepheid calibrations. Weuse both B and I-band magnitudes. The Spaenhauer diagram method is usedto correct for the Malmquist bias. We give the equations for theconstruction of this diagram. We analyze the apparent Hubble constant indifferent regions around Virgo and obtain simultaneously the Local Groupinfall and the unperturbed Hubble constant. We found:[VLG-infall = 208 ± 9 km s-1] [\log H =1.82 ± 0.04 (H ≈ 66 ± 6 km s-1Mpc-1).] The front side and backside infalls can be seenaround Virgo and Fornax. In the direction of Virgo the comparison ismade with the Peebles' model. We obtain: [vinfall} =CVirgo/r0.9 ± 0.2] withCVirgo=2800 for Virgo and CFornax=1350 for Fornax,with the adopted units (km s-1 and Mpc). We obtain thefollowing mean distance moduli: [μVirgo=31.3 ± 0.2(r=18 Mpc )] [μFornax=31.7 ± 0.3 (r=22 Mpc). ] Allthese quantities form an accurate and coherent system. Full Table 2 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/57
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