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Stellar Populations in Nearby Lenticular Galaxies
We have obtained two-dimensional spectral data for a sample of 58 nearbyS0 galaxies with the Multi-Pupil Fiber/Field Spectrograph of the 6 mtelescope of the Special Astrophysical Observatory of the RussianAcademy of Sciences. The Lick indices Hβ, Mg b, and arecalculated separately for the nuclei and for the bulges taken as therings between R=4'' and 7", and the luminosity-weighted ages,metallicities, and Mg/Fe ratios of the stellar populations are estimatedby comparing the data to single stellar population (SSP) models. Fourtypes of galaxy environments are considered: clusters, centers ofgroups, other places in groups, and the field. The nuclei are found tobe on average slightly younger than the bulges in any type ofenvironment, and the bulges of S0 galaxies in sparse environments areyounger than those in dense environments. The effect can be partlyattributed to the well-known age correlation with the stellar velocitydispersion in early-type galaxies (in our sample the galaxies in sparseenvironments are on average less massive than those in denseenvironments), but for the most massive S0 galaxies, withσ*=170-220 km s-1, the age dependence on theenvironment is still significant at the confidence level of 1.5 σ.Based on observations collected with the 6 m telescope (BTA) at theSpecial Astrophysical Observatory (SAO) of the Russian Academy ofSciences (RAS).
| Low-Luminosity Active Galaxies and Their Central Black Holes
Central black hole masses for 117 spiral galaxies representingmorphological stages S0/a through Sc and taken from the largespectroscopic survey of Ho et al. are derived using Ks-banddata from the Two Micron All Sky Survey. Black hole masses are foundusing a calibrated black hole-Ks bulge luminosity relation,while bulge luminosities are measured by means of a two-dimensionalbulge-disk decomposition routine. The black hole masses are correlatedagainst a variety of parameters representing properties of the nucleusand host galaxy. Nuclear properties such as line width (FWHM [N II]), aswell as emission-line ratios (e.g., [O III]/Hβ, [O I]/Hα, [NII]/Hα, and [S II]/Hα), show a very high degree ofcorrelation with black hole mass. The excellent correlation with linewidth supports the view that the emission-line gas is in virialequilibrium with either the black hole or bulge potential. The very goodemission-line ratio correlations may indicate a change in ionizingcontinuum shape with black hole mass in the sense that more massiveblack holes generate harder spectra. Apart from theinclination-corrected rotational velocity, no excellent correlations arefound between black hole mass and host galaxy properties. Significantdifferences are found between the distributions of black hole masses inearly-, mid-, and late-type spiral galaxies (subsamples A, B, and C) inthe sense that early-type galaxies have preferentially larger centralblack holes, consistent with observations that Seyfert galaxies arefound preferentially in early-type systems. The line width distributionsshow a marked difference among subsamples A, B, and C in the sense thatearlier type galaxies have larger line widths. There are also cleardifferences in line ratios between subsamples A+B and C that likely arerelated to the level of ionization in the gas. Finally, aKs-band Simien & de Vaucouleurs diagram shows excellentagreement with the original B-band relation, although there is a largedispersion at a given morphological stage.
| A Survey of Merger Remnants. II. The Emerging Kinematic and Photometric Correlations
This paper is the second in a series exploring the properties of 51optically selected, single-nuclei merger remnants. Spectroscopic datahave been obtained for a subsample of 38 mergers and combined withpreviously obtained infrared photometry to test whether mergers exhibitthe same correlations as elliptical galaxies among parameters such asstellar luminosity and distribution, central stellar velocity dispersion(σ0), and metallicity. Paramount to the study is totest whether mergers lie on the fundamental plane. Measurements ofσ0 have been made using the Ca triplet absorption lineat 8500 Å for all 38 mergers in the subsample. Additionalmeasurements of σ0 were made for two of the mergers inthe subsample using the CO absorption line at 2.29 μm. The resultsindicate that mergers show a strong correlation among the parameters ofthe fundamental plane but fail to show a strong correlation betweenσ0 and metallicity (Mg2). In contrast toearlier studies, the σ0 values of the mergers areconsistent with objects that lie somewhere between intermediate-mass andluminous giant elliptical galaxies. However, the discrepancies withearlier studies appear to correlate with whether the Ca triplet or COabsorption lines are used to derive σ0, with the latteralmost always producing smaller values. Finally, the photometric andkinematic data are used to demonstrate for the first time that thecentral phase-space densities of mergers are equivalent to those inelliptical galaxies. This resolves a long-standing criticism of themerger hypothesis.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
| On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies
We investigate the relation between X-ray nuclear emission, opticalemission line luminosities and black hole masses for a sample of 47Seyfert galaxies. The sample, which has been selected from the Palomaroptical spectroscopic survey of nearby galaxies (Ho et al. 1997a, ApJS,112, 315), covers a wide range of nuclear powers, from L2-10keV ~ 1043 erg/s down to very low luminosities(L2-10 keV ~ 1038 erg/s). Best available data fromChandra, XMM-Newton and, in a few cases, ASCA observations have beenconsidered. Thanks to the good spatial resolution available from theseobservations and a proper modeling of the various spectral components,it has been possible to obtain accurate nuclear X-ray luminosities notcontaminated by off-nuclear sources and/or diffuse emission. X-rayluminosities have then been corrected taking into account the likelycandidate Compton thick sources, which are a high fraction (>30%)among type 2 Seyferts in our sample. The main result of this study isthat we confirm strong linear correlations between 2-10 keV,[OIII]λ5007, Hα luminosities which show the same slope asquasars and luminous Seyfert galaxies, independent of the level ofnuclear activity displayed. Moreover, despite the wide range ofEddington ratios (L/L_Edd) tested here (six orders of magnitude, from0.1 down to ~10-7), no correlation is found between the X-rayor optical emission line luminosities and the black hole mass. Ourresults suggest that Seyfert nuclei in our sample are consistent withbeing a scaled-down version of more luminous AGN.
| How large are the bars in barred galaxies?
I present a study of the sizes (semimajor axes) of bars in discgalaxies, combining a detailed R-band study of 65 S0-Sb galaxies withthe B-band measurements of 70 Sb-Sd galaxies from Martin (1995). As hasbeen noted before with smaller samples, bars in early-type (S0-Sb)galaxies are clearly larger than bars in late-type (Sc-Sd) galaxies;this is true both for relative sizes (bar length as fraction ofisophotal radius R25 or exponential disc scalelength h) andabsolute sizes (kpc). S0-Sab bars extend to ~1-10 kpc (mean ~ 3.3 kpc),~0.2-0.8R25 (mean ~ 0.38R25) and ~0.5-2.5h (mean ~1.4h). Late-type bars extend to only ~0.5-3.5 kpc,~0.05-0.35R25 and 0.2-1.5h their mean sizes are ~1.5 kpc, ~0.14R25 and ~0.6h. Sb galaxies resemble earlier-type galaxiesin terms of bar size relative to h; their smallerR25-relative sizes may be a side effect of higher starformation, which increases R25 but not h. Sbc galaxies form atransition between the early- and late-type regimes. For S0-Sbcgalaxies, bar size correlates well with disc size (both R25and h); these correlations are stronger than the known correlation withMB. All correlations appear to be weaker or absent forlate-type galaxies; in particular, there seems to be no correlationbetween bar size and either h or MB for Sc-Sd galaxies.Because bar size scales with disc size and galaxy magnitude for mostHubble types, studies of bar evolution with redshift should selectsamples with similar distributions of disc size or magnitude(extrapolated to present-day values); otherwise, bar frequencies andsizes could be mis-estimated. Because early-type galaxies tend to havelarger bars, resolution-limited studies will preferentially find bars inearly-type galaxies (assuming no significant differential evolution inbar sizes). I show that the bars detected in Hubble Space Telescope(HST) near-infrared(IR) images at z~ 1 by Sheth et al. have absolutesizes consistent with those in bright, nearby S0-Sb galaxies. I alsocompare the sizes of real bars with those produced in simulations anddiscuss some possible implications for scenarios of secular evolutionalong the Hubble sequence. Simulations often produce bars as large as(or larger than) those seen in S0-Sb galaxies, but rarely any as smallas those in Sc-Sd galaxies.
| Advanced mergers of galaxies: luminosity profiles and dynamics
We have analyzed the near-IR Ks-band data from the 2MASS archivaldatabase for a large sample of twenty-seven galaxies that show signs ofinteraction but have a single nucleus. Surprisingly, half of theseadvanced mergers of galaxies show luminosity profiles which have anouter exponential fall-off with radius, as in a spiral galaxy (Chitreand Jog 2002). The kinematical data for two of these, Arp 224 and Arp214, available from the HYPERCAT database were used and these showkinematics similar to elliptical galaxies with the random motiondominating the rotation (Jog and Chitre 2002). The origin of the mixedproperties shown by these mergers is a puzzle. To understand thesesystems, we have recently studied the dynamics of mergers via N-bodysimulations for unequal-mass mergers covering a new range of galaxy massratios 4:1-10:1 (Bournaud, Combes, and Jog 2004). We show that suchmergers naturally result in remnants that have the mixed properties aswe have observed from the 2MASS data analysis. The transition betweenelliptical and disk-like remnants is found to occur over a narrow rangeof galaxy mass ratios 3:1-4.5:1 (Bournaud, Jog and Combes 2005).
| The Westerbork HI survey of spiral and irregular galaxies. III. HI observations of early-type disk galaxies
We present Hi observations of 68 early-type disk galaxies from the WHISPsurvey. They have morphological types between S0 and Sab and absoluteB-band magnitudes between -14 and -22. These galaxies form the massive,high surface-brightness extreme of the disk galaxy population, few ofwhich have been imaged in Hi before. The Hi properties of the galaxiesin our sample span a large range; the average values of MHI/LB and DH I/D25 are comparableto the ones found in later-type spirals, but the dispersions around themean are larger. No significant differences are found between the S0/S0aand the Sa/Sab galaxies. Our early-type disk galaxies follow the same Himass-diameter relation as later-type spiral galaxies, but theireffective Hi surface densities are slightly lower than those found inlater-type systems. In some galaxies, distinct rings of Hi emissioncoincide with regions of enhanced star formation, even though theaverage gas densities are far below the threshold of star formationderived by Kennicutt (1989, ApJ, 344, 685). Apparently, additionalmechanisms, as yet unknown, regulate star formation at low surfacedensities. Many of the galaxies in our sample have lopsided gasmorphologies; in most cases this can be linked to recent or ongoinginteractions or merger events. Asymmetries are rare in quiescentgalaxies. Kinematic lopsidedness is rare, both in interacting andisolated systems. In the appendix, we present an atlas of the Hiobservations: for all galaxies we show Hi surface density maps, globalprofiles, velocity fields and radial surface density profiles.
| Radio sources in low-luminosity active galactic nuclei. IV. Radio luminosity function, importance of jet power, and radio properties of the complete Palomar sample
We present the completed results of a high resolution radio imagingsurvey of all ( 200) low-luminosity active galactic nuclei (LLAGNs) andAGNs in the Palomar Spectroscopic Sample of all ( 488) bright northerngalaxies. The high incidences of pc-scale radio nuclei, with impliedbrightness temperatures ≳107 K, and sub-parsec jetsargue for accreting black holes in ≳50% of all LINERs andlow-luminosity Seyferts; there is no evidence against all LLAGNs beingmini-AGNs. The detected parsec-scale radio nuclei are preferentiallyfound in massive ellipticals and in type 1 nuclei (i.e. nuclei withbroad Hα emission). The radio luminosity function (RLF) of PalomarSample LLAGNs and AGNs extends three orders of magnitude below, and iscontinuous with, that of “classical” AGNs. We find marginalevidence for a low-luminosity turnover in the RLF; nevertheless LLAGNsare responsible for a significant fraction of present day massaccretion. Adopting a model of a relativistic jet from Falcke &Biermann, we show that the accretion power output in LLAGNs is dominatedby the kinetic power in the observed jets rather than the radiatedbolometric luminosity. The Palomar LLAGNs and AGNs follow the samescaling between jet kinetic power and narrow line region (NLR)luminosity as the parsec to kilo-parsec jets in powerful radio galaxies.Eddington ratios {l_Edd} (=L_Emitted/L_Eddington) of≤10-1{-}10-5 are implied in jet models of theradio emission. We find evidence that, in analogy to Galactic black holecandidates, LINERs are in a “low/hard” state (gas poornuclei, low Eddington ratio, ability to launch collimated jets) whilelow-luminosity Seyferts are in a “high” state (gas richnuclei, higher Eddington ratio, less likely to launch collimated jets).In addition to dominating the radiated bolometric luminosity of thenucleus, the radio jets are energetically more significant thansupernovae in the host galaxies, and are potentially able to depositsufficient energy into the innermost parsecs to significantly slow thegas supply to the accretion disk.
| Bar-induced perturbation strengths of the galaxies in the Ohio State University Bright Galaxy Survey - I
Bar-induced perturbation strengths are calculated for a well-definedmagnitude-limited sample of 180 spiral galaxies, based on the Ohio StateUniversity Bright Galaxy Survey. We use a gravitational torque method,the ratio of the maximal tangential force to the mean axisymmetricradial force, as a quantitative measure of the bar strength. Thegravitational potential is inferred from an H-band light distribution byassuming that the M/L ratio is constant throughout the disc. Galaxiesare deprojected using orientation parameters based on B-band images. Inorder to eliminate artificial stretching of the bulge, two-dimensionalbar-bulge-disc decomposition has been used to derive a reliable bulgemodel. This bulge model is subtracted from an image, the disc isdeprojected assuming it is thin, and then the bulge is added back byassuming that its mass distribution is spherically symmetric. We findthat removing the artificial bulge stretch is important especially forgalaxies having bars inside large bulges. We also find that the massesof the bulges can be significantly overestimated if bars are not takeninto account in the decomposition.Bars are identified using Fourier methods by requiring that the phasesof the main modes (m= 2, m= 4) are maintained nearly constant in the barregion. With such methods, bars are found in 65 per cent of the galaxiesin our sample, most of them being classified as SB-type systems in thenear-infrared by Eskridge and co-workers. We also suggest that as muchas ~70 per cent of the galaxies classified as SAB-types in thenear-infrared might actually be non-barred systems, many of them havingcentral ovals. It is also possible that a small fraction of the SAB-typegalaxies have weak non-classical bars with spiral-like morphologies.
| Stacking Searches for Gamma-Ray Emission above 100 MeV from Radio and Seyfert Galaxies
The EGRET telescope on board Compton Gamma Ray Observatory detected morethan 60 sources of high-energy gamma radiation associated with activegalactic nuclei (AGNs). All but one of those belong to the blazarsubclass; the only exception is the nearby radio galaxy Centaurus A.Since there is no obvious reason other than proximity to expect Cen A tobe the only nonblazar AGN emitting in high-energy gamma rays, we haveutilized the ``stacking'' technique to search for emission above 100 MeVfrom two nonblazar AGN subclasses, radio galaxies and Seyfert galaxies.Maps of gamma-ray counts, exposure, and diffuse background have beencreated, then co-added in varying numbers based on sorts by redshift, 5GHz flux density, and optical brightness, and finally tested forgamma-ray emission. No detection significance greater than 2 σ hasbeen found for any subclass, sorting parameter, or number of objectsco-added. Monte Carlo simulations have also been performed to validatethe technique and estimate the significance of the results.
| A Deep K-Band Photometric Survey of Merger Remnants
We present K-band photometry for 51 candidate merger remnants to assessthe viability of whether spiral-spiral mergers can produce bona fideelliptical galaxies. Using both the de Vaucouleurs r1/4 andSérsic r1/n fitting laws, it is found that the stellarcomponent in a majority of the galaxies in the sample has undergoneviolent relaxation. However, the sample shows evidence for incompletephase mixing. The analysis also indicates the presence of ``excesslight'' in the surface brightness profiles of nearly one-third of themerger remnants. Circumstantial evidence suggests that this is due tothe effects of a starburst induced by the dissipative collapse of thegas. The integrated light of the galaxies also shows that mergers canmake L* elliptical galaxies, in contrast to earlier infrared studies.The isophotal shapes and related structural parameters are alsodiscussed, including the fact that 70% of the sample show evidence fordisky isophotes. The data and results presented are part of a largerphotometric and spectroscopic campaign to thoroughly investigate a largesample of mergers in the local universe.
| Inner Polar Rings in Regular Lenticular Galaxies
We have investigated a sample of S0 galaxies, mostly with circumnucleardust lanes orthogonal to their major axes, chosen from Hubble SpaceTelescope Wide Field Planetary Camera 2 images. Two-dimensionalspectroscopy undertaken with the Multipupil Fiber Spectrograph of the 6m telescope of the Special Astrophysical Observatory of the RussianAcademy of Sciences has revealed that indeed the ionized gas in thecenters of these eight lenticular galaxies rotate in the planes nearlyorthogonal to the rotation (and symmetry) planes of their centralstellar components. Although almost all the galaxies are located indense environments, an external origin of this rotation plane tilt isnot obvious because all the galaxies but one are known to have extendedH I disks, and in two cases where the angular resolution of H Iobservations allows, we find orthogonality of the external H I and innerionized gas disks. We discuss a possible relation of the inner gas polarrings to a triaxiality of galactic potential. The stellar populations inthe nuclei of all but two galaxies are very old, which excludes recentstar formation bursts and proves that the polar orbits of thecircumnuclear gas are rather stable. In the nuclei of NGC 2655 and NGC4111, we have found signatures of star formation bursts some 1.5-2 Gyrago. This finding can be related to very central gas in NGC 2655, whichis coplanar to the circumnuclear stellar disk and to radial gas inflowin NGC 4111; just these gas reservoirs and not the polar rings may beresponsible for fueling nuclear star formation.Partly based on observations collected with the 6 m telescope at theSpecial Astrophysical Observatory of the Russian Academy of Sciences.
| Inner-truncated Disks in Galaxies
We present an analysis of the disk brightness profiles of 218 spiral andlenticular galaxies. At least 28% of disk galaxies exhibit innertruncations in these profiles. There are no significant trends oftruncation incidence with Hubble type, but the incidence among barredsystems is 49%, more than 4 times that for nonbarred galaxies. However,not all barred systems have inner truncations, and not allinner-truncated systems are currently barred. Truncations represent areal dearth of disk stars in the inner regions and are not an artifactof our selection or fitting procedures nor the result of obscuration bydust. Disk surface brightness profiles in the outer regions are wellrepresented by simple exponentials for both truncated and nontruncateddisks. However, truncated and nontruncated systems have systematicallydifferent slopes and central surface brightness parameters for theirdisk brightness distributions. Truncation radii do not appear tocorrelate well with the sizes or brightnesses of the bulges. Thissuggests that the low angular momentum material apparently missing fromthe inner disk was not simply consumed in forming the bulge population.Disk parameters and the statistics of bar orientations in our sampleindicate that the missing stars of the inner disk have not simply beenredistributed azimuthally into bar structures. The sharpness of thebrightness truncations and their locations with respect to othergalactic structures suggest that resonances associated with diskkinematics, or tidal interactions with the mass of bulge stars, might beresponsible for this phenomenon.
| 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
| UV and FIR selected samples of galaxies in the local Universe. Dust extinction and star formation rates
We have built two samples of galaxies selected at 0.2 μm (hereafterUV) and 60 μm (hereafter FIR) covering a sky area of 35.36deg2. The UV selected sample contains 25 galaxies brighterthan AB0.2=17. All of them, but one elliptical, are detectedat 60 μm with a flux density larger or equal to 0.2 Jy. The UV countsare significantly lower than the Euclidean extrapolation towardsbrighter fluxes of previous determinations. The FIR selected samplecontains 42 galaxies brighter than f60=0.6 Jy. Except fourgalaxies, all of them have a UV counterpart at the limiting magnitudeAB0.2=20.3 mag. The mean extinction derived from the analysisof the FIR to UV flux ratio is 1 mag for the UV selected sample and2 mag for the FIR selected one. For each sample we compare severalindicators of the recent star formation rate (SFR) based on the FIRand/or the UV emissions. We find linear relationships with slopes closeto unity between the different SFR indicator, which means that, over thewhole converting offset. Various absolute calibrations for both samplesare discussed in this paper. A positive correlation between extinctionand SFR is found when both samples are considered together although witha considerable scatter. A similar result is obtained when using the SFRnormalized to the optical surface of the galaxies.Tables 3, 4 and Fig. 1 are only available in electronic form athttp://www.edpsciences.org
| The Hα galaxy survey. I. The galaxy sample, Hα narrow-band observations and star formation parameters for 334 galaxies
We discuss the selection and observations of a large sample of nearbygalaxies, which we are using to quantify the star formation activity inthe local Universe. The sample consists of 334 galaxies across allHubble types from S0/a to Im and with recession velocities of between 0and 3000 km s-1. The basic data for each galaxy are narrowband H\alpha +[NII] and R-band imaging, from which we derive starformation rates, H\alpha +[NII] equivalent widths and surfacebrightnesses, and R-band total magnitudes. A strong correlation is foundbetween total star formation rate and Hubble type, with the strongeststar formation in isolated galaxies occurring in Sc and Sbc types. Moresurprisingly, no significant trend is found between H\alpha +[NII]equivalent width and galaxy R-band luminosity. More detailed analyses ofthe data set presented here will be described in subsequent papers.Based on observations made with the Jacobus Kapteyn Telescope operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.The full version of Table \ref{tab3} is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/23 Reduced image datafor this survey can be downloaded fromhttp://www.astro.livjm.ac.uk/HaGS/
| An Imaging Survey of Early-Type Barred Galaxies
This paper presents the results of a high-resolution imaging survey,using both ground-based and Hubble Space Telescope images, of a completesample of nearby barred S0-Sa galaxies in the field, with a particularemphasis on identifying and measuring central structures within thebars: secondary bars, inner disks, nuclear rings and spirals, andoff-plane dust. A discussion of the frequency and statistical propertiesof the various types of inner structures has already been published.Here we present the data for the individual galaxies and measurements oftheir bars and inner structures. We set out the methods we use to findand measure these structures, and how we discriminate between them. Inparticular, we discuss some of the deficiencies of ellipse fitting ofthe isophotes, which by itself cannot always distinguish between bars,rings, spirals, and dust, and which can produce erroneous measurementsof bar sizes and orientations.
| Chandra Snapshot Observations of Low-Luminosity Active Galactic Nuclei with a Compact Radio Source
The results of Chandra snapshot observations of 11 low-ionizationnuclear emission-line regions (LINERs), three low-luminosity Seyfertgalaxies, and one H II-LINER transition object are presented. Our sampleconsists of all the objects with a flat- or inverted-spectrum, compactradio core in the Very Large Array survey of 48 low-luminosity AGNs(LLAGNs) by Nagar and coworkers in 2000. An X-ray nucleus is detected inall galaxies except one, and their X-ray luminosities are in the range5×1038-8×1041 ergs s-1. TheX-ray spectra are generally steeper than expected from thermalbremsstrahlung emission from an advection-dominated accretion flow. TheX-ray-to-Hα luminosity ratios for 11 of 14 objects are in goodagreement, with the value characteristic of LLAGNs and more luminousAGNs, and indicate that their optical emission lines are predominantlypowered by an LLAGN. For three objects, this ratio is less thanexpected. Comparing with properties in other wavelengths, we find thatthese three galaxies are most likely to be heavily obscured AGNs. We usethe ratio RX=νLν(5 GHz)/LX, whereLX is the luminosity in the 2-10 keV band, as a measure ofradio loudness. In contrast to the usual definition of radio loudness[Ro=Lν(5 GHz)/Lν(B)],RX can be used for heavily obscured(NH>~1023 cm-2, AV>50mag) nuclei. Further, with the high spatial resolution of Chandra, thenuclear X-ray emission of LLAGNs is often easier to measure than thenuclear optical emission. We investigate the values of RX forLLAGNs, luminous Seyfert galaxies, quasars, and radio galaxies andconfirm the suggestion that a large fraction of LLAGNs are radio-loud.
| High-energy sources before INTEGRAL. INTEGRAL reference catalog
We describe the INTEGRAL reference catalog which classifies previouslyknown bright X-ray and gamma-ray sources before the launch of INTEGRAL.These sources are, or have been at least once, brighter than ~ 1 mCrababove 3 keV, and are expected to be detected by INTEGRAL. This catalogis being used in the INTEGRAL Quick Look Analysis to discover newsources or significantly variable sources. We compiled several publishedX-ray and gamma-ray catalogs, and surveyed recent publications for newsources. Consequently, there are 1122 sources in our INTEGRAL referencecatalog. In addition to the source positions, we show an approximatespectral model and expected flux for each source, based on which wederive expected INTEGRAL counting rates. Assuming the default instrumentperformances and at least ~ 105 s exposure time for anypart of the sky, we expect that INTEGRAL will detect at least ~ 700sources below 10 keV and ~ 400 sources above 20 keV over the missionlife.The Catalog is available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/411/L59
| `Radio-loud' low luminosity AGN
Our VLBA survey of nearby bright LLAGN has found high brightnesstemperature (>108 K) radio cores in 16 of 17 objectsobserved, with four of them even hosting parsec scale jets, stronglysuggesting that at least 20% of LLAGN are accretion powered. Few LLAGNshow the steep radio spectra expected in an advection dominatedaccretion flow (ADAF). However, the X-ray to radio, and Mbhto radio relationships, are consistent with the predictions of ADAF's.The compact cores and flat to inverted spectral indices in some LLAGNare consistent with the predictions of the scaled jet model of Falckeand collaborators. Plotted on a log P2 cm vs. logLemission-line diagram, all LLAGN in elliptical hosts, andmost other LINERs and Transition objects which host compact radio cores,appear more closely related to radio galaxies than to `classical'Seyferts.
| Bar strengths in spiral galaxies estimated from 2MASS images
Non-axisymmetric forces are presented for a sample of 107 spiralgalaxies, of which 31 are barred (SB) and 53 show nuclear activity. As adata base we use JHK images from the 2 Micron All-sky Survey, and thenon-axisymmetries are characterized by the ratio of the tangential forceto the mean axisymmetric radial force field, following Buta & Block.Bar strengths have an important role in many extragalactic problems andtherefore it is important to verify that the different numerical methodsapplied for calculating the forces give mutually consistent results. Weapply both direct Cartesian integration and a polar grid integrationutilizing a limited number of azimuthal Fourier components of density.We find that the bar strength is independent of the method used toevaluate the gravitational potential. However, because of thedistance-dependent smoothing by Fourier decomposition, the polar methodis more suitable for weak and noisy images. The largest source ofuncertainty in the derived bar strength appears to be the uncertainty inthe vertical scaleheight, which is difficult to measure directly formost galaxies. On the other hand, the derived bar strength is ratherinsensitive to the possible gradient in the vertical scaleheight of thedisc or to the exact model of the vertical density distribution,provided that the same effective vertical dispersion is assumed in allmodels. In comparison with the pioneering study by Buta & Block, thebar strength estimate is improved here by taking into account thedependence of the vertical scaleheight on the Hubble type: we find thatfor thin discs bar strengths are stronger than for thick discs by anamount that may correspond to as much as one bar strength class. Weconfirm the previous result by Buta and co-workers showing that thedispersion in bar strength is large among all the de Vaucouleurs opticalbar classes. In the near-infrared 40 per cent of the galaxies in oursample have bars (showing constant phases in the m= 2 Fourier amplitudesin the bar region), while in the optical band one-third of these barsare obscured by dust. Significant non-axisymmetric forces can also beinduced by the spiral arms, generally in the outer parts of the galacticdiscs, which may have important implications on galaxy evolution.Possible biases of the selected sample are also studied: we find thatthe number of bars identified drops rapidly when the inclination of thegalactic disc is larger than 50°. A similar bias is found in theThird Reference Catalogue of Bright Galaxies, which might be of interestwhen comparing bar frequencies at high and low redshifts.
| X-Ray Properties of LINERs and Low-Luminosity Seyfert Galaxies Observed with ASCA. I. Observations and Results
This paper presents a comprehensive study of the X-ray properties oflow-ionization nuclear emission-line regions (LINERs) and low-luminositySeyfert galaxies based on observations obtained with the ASCA satellite.We analyzed data of 53 observations of 21 LINERs and 17 low-luminositySeyferts. X-ray emission has been detected in all but one object. TheX-ray luminosities in the 2-10 keV band range from4×1039 to 5×1041 ergs s-1,which are 1-3 orders of magnitude smaller than in classical Seyfertgalaxies. The X-ray spectra of most objects are well described by acanonical model which consists of (1) a soft component from a thermalplasma with kT<1 keV and (2) a hard component represented by a powerlaw with a photon index of Γ~1.8 or thermal bremsstrahlungemission with kT~10 keV. Several objects do not require the soft thermalcomponent, and their continua are well fitted by a single power-lawmodel. Some objects show heavy absorption with column densities inexcess of 1023 cm-2. We detect in several objectsFe K line emission with equivalent widths ranging from 50 eV to 2 keV.Variability on timescales less than a day is uncommon in our sample. Bycomparing multiple observations made with ASCA or with published 2-10keV observations from other satellites, we show that at least eightobjects are variable on timescales of a week to several years. We findthat the morphologies of many objects, both in the soft and hard bands,are consistent with being pointlike relative to the telescopepoint-spread function; a few are clearly extended in either or bothenergy bands. The second paper of this series will discuss the physicalinterpretation of the X-ray emission and its implications forlow-luminosity active galactic nuclei.
| Far-Infrared Census of Starburst-Seyfert Connection
Far-infrared flux densities are newly extracted from the IRAS databasefor the Revised Shapley-Ames and CfA complete samples of Seyfertgalaxies. These data are used to classify the Seyfert galaxies intothose where the far-infrared continuum emission is dominated by theactive galactic nucleus (AGN), circumnuclear starburst, or host galaxy.While AGN-dominant objects consist of comparable numbers of Seyfert 1and 2 galaxies, starburst- and host-dominant objects consistpreferentially of Seyfert 2 galaxies. Thus, in addition to the dustytorus, the circumnuclear starburst region and host galaxy are importantin hiding the broad-line region. Morphologically, starburst-dominantSeyfert galaxies are of later types and more strongly interacting thanAGN-dominant Seyfert galaxies. In a later type galaxy, the AGN centralengine has a lower Eddington luminosity, and the gaseous content ishigher. The gas is efficiently supplied to the starburst via agalaxy-galaxy interaction. Morphologies of host-dominant Seyfertgalaxies are of various types. Since starbursts in Seyfert galaxies areolder than those in classical starburst galaxies, we propose anevolution from starburst to starburst-dominant Seyfert to host-dominantSeyfert for a late-type galaxy. An evolution from AGN-dominant Seyfertto host-dominant Seyfert is proposed for an early-type galaxy. Thesesequences have durations of a few times 108 yr and occurrepeatedly within a galaxy during its evolution from a late type to anearly type.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| Double Bars, Inner Disks, and Nuclear Rings in Early-Type Disk Galaxies
We present results from a survey of an unbiased sample of 38 early-type(S0-Sa), low-inclination, optically barred galaxies in the field, usingimages both from the ground and from space. Our goal was to find andcharacterize central stellar and gaseous structures: secondary bars,inner disks, and nuclear rings. We find that bars inside bars aresurprisingly common: at least one-quarter of the sample galaxies(possibly as many as 40%) are double barred, with no preference forHubble type or the strength of the primary bar. A typical secondary baris ~12% of the size of its primary bar and extends to 240-750 pc inradius. Secondary bars are not systematically either parallel orperpendicular to the primary; we see cases where they lead the primarybar in rotation and others where they trail, which supports thehypothesis that the two bars of a double-bar system rotateindependently. We see no significant effect of secondary bars on nuclearactivity: our double-barred galaxies are no more likely to harbor aSeyfert or LINER nucleus than our single-barred galaxies. We findkiloparsec-scale inner disks in at least 20% of our sample; they occuralmost exclusively in S0 galaxies. These disks are on average 20% thesize of their host bar and show a wider range of relative sizes than dosecondary bars. Nuclear rings are present in about a third of oursample. Most of these rings are dusty, sites of current or recent starformation, or both; such rings are preferentially found in Sa galaxies.Three S0 galaxies (8% of the sample, but 15% of the S0's) appear to havepurely stellar nuclear rings, with no evidence for dust or recent starformation. The fact that these central stellar structures are so commonindicates that the inner regions of early-type barred galaxies typicallycontain dynamically cool and disklike structures. This is especiallytrue for S0 galaxies, where secondary bars, inner disks, and/or stellarnuclear rings are present at least two-thirds of the time. If weinterpret nuclear rings, secondary bars, and (possibly) inner disks andnuclear spirals as signs of inner Lindblad resonances (ILRs), thenbetween one and two-thirds of barred S0-Sa galaxies show evidence forILRs.
| Radio sources in low-luminosity active galactic nuclei. III. ``AGNs'' in a distance-limited sample of ``LLAGNs''
This paper presents the results of a high resolution radio imagingsurvey of all known (96) low-luminosity active galactic nuclei (LLAGNs)at D <= 19 Mpc. We first report new 2 cm (150 mas resolution usingthe VLA) and 6 cm (2 mas resolution using the VLBA) radio observationsof the previously unobserved nuclei in our samples and then presentresults on the complete survey. We find that almost half of all LINERsand low-luminosity Seyferts have flat-spectrum radio cores when observedat 150 mas resolution. Higher (2 mas) resolution observations of aflux-limited subsample have provided a 100% (16 of 16) detection rate ofpc-scale radio cores, with implied brightness temperatures gtrsim108 K. The five LLAGNs with the highest core radio fluxesalso have pc-scale ``jets''. Compact radio cores are almost exclusivelyfound in massive ellipticals and in type 1 nuclei (i.e. nuclei withbroad Hα emission). Only a few ``transition'' nuclei have compactradio cores; those detected in the radio have optical emission-linediagnostic ratios close to those of LINERs/Seyferts. This indicates thatsome transition nuclei are truly composite Seyfert/LINER+H II regionnuclei, with the radio core power depending on the strength of theformer component. The core radio power is correlated with the nuclearoptical ``broad'' Hα luminosity, the nuclear optical ``narrow''emission-line luminosity and width, and with the galaxy luminosity. Inthese correlations LLAGNs fall close to the low-luminosityextrapolations of more powerful AGNs. The scalings suggest that many ofthe radio-non-detected LLAGNs are simply lower power versions of theradio-detected LLAGNs. The ratio of core radio power to nuclear opticalemission-line luminosity increases with increasing bulge luminosity forall LLAGNs. Also, there is evidence that the luminosity of the diskcomponent of the galaxy is correlated with the nuclear emission-lineluminosity (but not the core radio power). About half of all LLAGNs withmultiple epoch data show significant inter-year radio variability.Investigation of a sample of ~ 150 nearby bright galaxies, most of themLLAGNs, shows that the nuclear (<=150 mas size) radio power isstrongly correlated with both the black hole mass and the galaxy bulgeluminosity; linear regression fits to all ~ 150 galaxies give: logP2 cm = 1.31(+/-0.16) log {MMDO} + 8.77 and logP2 cm = 1.89(+/-0.21) log LB(bulge) -0.17. Lowaccretion rates (<=10-2-10-3 of the Eddingtonrate) are implied in both advection- and jet-type models. In brief, allevidence points towards the presence of accreting massive black holes ina large fraction, perhaps all, of LLAGNs, with the nuclear radioemission originating in either the accretion inflow onto the massiveblack hole or from jets launched by this black hole-accretion disksystem.
| Luminosity profiles of advanced mergers of galaxies using 2MASS data
A sample of 27 disturbed galaxies that show signs of interaction buthave a single nucleus were selected from the Arp and the Arp-Madorecatalogues. For these, the Ks band images from the Two MicronAll Sky Survey (2MASS) are analysed to obtain their radial luminosityprofiles and other structural parameters. We find that in spite of theirsimilar optical appearance, the sample galaxies vary in their dynamicalproperties, and fall into two distinct classes. The first class consistsof galaxies which can be described by a single r1/4 law andthe second class consists of galaxies that show an outer exponentialdisk. A few galaxies that have disturbed profiles cannot be fit intoeither of the above classes. However, all the galaxies are similar inall other parameters such as the far-infrared colours, the molecularhydrogen content and the central velocity dispersion. Thus, thedynamical parameters of these sets seem to be determined by the ratio ofthe initial masses of the colliding galaxies. We propose that thegalaxies in the first class result from a merger of spiral galaxies ofequal masses whereas the second class of galaxies results from a mergerof unequal mass galaxies. The few objects that do not fall into eithercategory show a disturbed luminosity profile and a wandering centre,which is indicative of these being unrelaxed mergers. Of the 27 galaxiesin our sample, 9 show elliptical-like profiles and 13 show an outerexponential. Interestingly, Arp 224, the second oldest merger remnant ofthe Toomre sequence shows an exponential disk in the outer parts.
| A morphological comparison between the central region in AGN and normal galaxies using HST data
We study the morphology of the central region of a sample of ActiveGalactic Nuclei (AGN) and a ``control'' sample of normal galaxies usingarchival observations of the WFPC2 instrument onboard the Hubble SpaceTelescope (HST). We use the ellipse fitting technique in order to get agood description of the inner ``smooth'' light distribution of thegalaxy. We then divide the observed galaxy image by the artificial imagefrom the fitted ellipses in order to detect morphological signatures inthe central region around the nucleus of the galaxy. We performquantitative comparisons of different subgroups of our sample ofgalaxies (according to the Hubble type and the nuclear activity of thegalaxies) by calculating the average amplitude of the structures thatare revealed with the ellipse fitting technique. Our main conclusionsare as follows: 1) All AGNs show significant structure in their inner100 pc and 1 kpc regions whose amplitude is similar in all of them,independent of the Hubble type of the host galaxy. 2) When consideringearly-type galaxies, non-AGN galaxies show no structure at all, contraryto what we find for AGN. 3) When considering late-type galaxies, bothAGN and non-AGN galaxies show significant structure in their centralregion. Our results are consistent with the hypothesis that allearly-type galaxies host a supermassive black hole, but only those thathave enough material in the central regions to fuel it show an activenucleus. The situation is more complicated in late-type galaxies. Eithernot all of them host a central black hole, or, in some of them, thematerial inside the innermost 100 pc region is not transported to thescales of the central engine for some reason, or the large amount of gasand dust hides the active nucleus from our sight. Based on observationsmade with the NASA/ESA Hubble Space Telescope, obtained from the dataarchive at the Space Telescope Science Institute. STScI is operated bythe Association of Universities for Research in Astronomy, Inc., underthe NASA contract NAS5-26555.
| Radio continuum and CO emission in star-forming galaxies
We combine the radio continuum images from the NRAO VLA Sky Survey withthe CO-line observations from the extragalactic CO survey of the FiveCollege Radio Astronomy Observatory to study the relationship betweenmolecular gas and the star formation rate within the disks of 180 spiralgalaxies at 45\arcsec resolution. We find a tight correlation betweenthese quantities. On average, the ratio between the radio continuum andthe CO emission is constant, within a factor of 3, both inside the samegalaxy and from galaxy to galaxy. The mean star formation efficiencydeduced from the radio continuum corresponds to convert 3.5% of theavailable molecular gas into stars on a time scale of 108 yrand depends weakly on general galaxy properties, such as Hubble type ornuclear activity. A comparison is made with another similar analysisperformed using the Halpha luminosity as star formationindicator. The overall agreement we find between the two studiesreinforces the use of the radio luminosity as star formation rateindicator not only on global but also on local scales.
| High-resolution radio observations of Seyfert galaxies in the extended 12-μm sample - II. The properties of compact radio components
We discuss the properties of compact nuclear radio components in Seyfertgalaxies from the extended 12-μm AGN sample of Rush et al. Our mainresults can be summarized as follows. Type 1 and type 2 Seyferts producecompact radio components which are indistinguishable in strength andaspect, indicating that their central engines are alike, as proposed bythe unification model. Infrared IRAS fluxes are more closely correlatedwith low-resolution radio fluxes than high-resolution radio fluxes,suggesting that they are dominated by kiloparsec-scale, extranuclearemission regions; extranuclear emission may be stronger in type 2Seyferts. Early-type Seyfert galaxies tend to have stronger nuclearradio emission than late-type Seyfert galaxies. V-shaped extendedemission-line regions, indicative of `ionization cones', are usuallyfound in sources with large, collimated radio outflows. Hidden broadlines are most likely to be found in sources with powerful nuclear radiosources. Type 1 and type 2 Seyferts selected by their IRAS 12-μm fluxdensities have well-matched properties.
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