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The ACS Virgo Cluster Survey. VIII. The Nuclei of Early-Type Galaxies
The ACS Virgo Cluster Survey is a Hubble Space Telescope program toobtain high-resolution imaging in widely separated bandpasses (F475W~gand F850LP~z) for 100 early-type members of the Virgo Cluster, spanninga range of ~460 in blue luminosity. We use this large, homogenous dataset to examine the innermost structure of these galaxies and tocharacterize the properties of their compact central nuclei. We presenta sharp upward revision in the frequency of nucleation in early-typegalaxies brighter than MB~-15 (66%<~fn<~82%)and show that ground-based surveys underestimated the number of nucleidue to surface brightness selection effects, limited sensitivity andpoor spatial resolution. We speculate that previously reported claimsthat nucleated dwarfs are more concentrated toward the center of Virgothan their nonnucleated counterparts may be an artifact of theseselection effects. There is no clear evidence from the properties of thenuclei, or from the overall incidence of nucleation, for a change atMB~-17.6, the traditional dividing point between dwarf andgiant galaxies. There does, however, appear to be a fundamentaltransition at MB~-20.5, in the sense that the brighter,``core-Sérsic'' galaxies lack resolved (stellar) nuclei. A searchfor nuclei that may be offset from the photocenters of their hostgalaxies reveals only five candidates with displacements of more than0.5", all of which are in dwarf galaxies. In each case, however, theevidence suggests that these ``nuclei'' are, in fact, globular clustersprojected close to the galaxy photocenter. Working from a sample of 51galaxies with prominent nuclei, we find a median half-light radius of=4.2 pc, with the sizes of individual nucleiranging from 62 pc down to <=2 pc (i.e., unresolved in our images) inabout a half-dozen cases. Excluding these unresolved objects, the nucleisizes are found to depend on nuclear luminosity according to therelation rh L0.50+/-0.03. Because the largemajority of nuclei are resolved, we can rule out low-level AGNs as anexplanation for the central luminosity excess in almost all cases. Onaverage, the nuclei are ~3.5 mag brighter than a typical globularcluster. Based on their broadband colors, the nuclei appear to have oldto intermediate age stellar populations. The colors of the nuclei ingalaxies fainter than MB~-17.6 are tightly correlated withtheir luminosities, and less so with the luminosities of their hostgalaxies, suggesting that their chemical enrichment histories weregoverned by local or internal factors. Comparing the nuclei to the``nuclear clusters'' found in late-type spiral galaxies reveals a closematch in terms of size, luminosity, and overall frequency. A formationmechanism that is rather insensitive to the detailed properties of thehost galaxy properties is required to explain this ubiquity andhomogeneity. The mean of the frequency function for thenucleus-to-galaxy luminosity ratio in our nucleated galaxies,=-2.49+/-0.09 dex (σ=0.59+/-0.10), isindistinguishable from that of the SBH-to-bulge mass ratio,=-2.61+/-0.07dex (σ=0.45+/-0.09), calculated in 23 early-type galaxies withdetected supermassive black holes (SBHs). We argue that the compactstellar nuclei found in many of our program galaxies are the low-masscounterparts of the SBHs detected in the bright galaxies. If thisinterpretation is correct, then one should think in terms of ``centralmassive objects''-either SBHs or compact stellar nuclei-that accompanythe formation of almost all early-type galaxies and contain a meanfraction ~0.3% of the total bulge mass. In this view, SBHs would be thedominant formation mode above MB~-20.5.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.
| 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).
| The ACS Virgo Cluster Survey. XI. The Nature of Diffuse Star Clusters in Early-Type Galaxies
We use HST ACS imaging of 100 early-type galaxies in the ACS VirgoCluster Survey to investigate the nature of diffuse star clusters(DSCs). Compared to globular clusters (GCs), these star clusters havelow luminosities (MV>-8) and a broad distribution of sizes(320 magarcsec-2). The median colors of diffuse star cluster systems(1.1
| The ACS Virgo Cluster Survey. IX. The Color Distributions of Globular Cluster Systems in Early-Type Galaxies
We present the color distributions of globular cluster (GC) systems for100 early-type galaxies observed in the ACS Virgo Cluster Survey, thedeepest and most homogeneous survey of this kind to date. On average,galaxies at all luminosities in our study (-22
| The Link between Star Formation and Accretion in LINERs: A Comparison with Other Active Galactic Nucleus Subclasses
We present archival high-resolution X-ray imaging observations of 25nearby LINERs observed by ACIS on board Chandra. This sample builds onour previously published proprietary and archival X-ray observations andincludes the complete set of LINERs with published black hole masses andFIR luminosities that have been observed by Chandra. Of the 82 LINERsobserved by Chandra, 41 (50%) display hard nuclear cores consistent withan AGN. The nuclear 2-10 keV luminosities of these AGN-LINERs range from~2×1038 to ~1×1044 ergss-1. Reinforcing our previous work, we find a significantcorrelation between the Eddington ratio,Lbol/LEdd, and the FIR luminosity,LFIR, as well as the IR brightness ratio,LFIR/LB, in the host galaxy of AGN-LINERs thatextends over 7 orders of magnitude in Lbol/LEdd.Combining our AGN-LINER sample with galaxies from other AGN subclasses,we find that this correlation is reinforced in a sample of 129 AGNs,extending over almost 9 orders of magnitude inLbol/LEdd. Using archival and previously publishedobservations of the 6.2 μm PAH feature from ISO, we find that it isunlikely that dust heating by the AGN dominates the FIR luminosity inour sample of AGNs. Our results may therefore imply a fundamental linkbetween the mass accretion rate (M˙), as measured by the Eddingtonratio, and the star formation rate (SFR), as measured by the FIRluminosity. Apart from the overall correlation, we find that thedifferent AGN subclasses occupy distinct regions in the LFIRand Lbol/LEdd plane. Assuming a constant radiativeefficiency for accretion, our results may imply a variation in theSFR/M˙ ratio as a function of AGN activity level, a result that mayhave significant consequences for our understanding of galaxy formationand black hole growth.
| Bar Diagnostics in Edge-On Spiral Galaxies. III. N-Body Simulations of Disks
Present in over 45% of local spirals, boxy and peanut-shaped bulges aregenerally interpreted as edge-on bars and may represent a key phase inbar evolution. Aiming to test such claims, the kinematic properties ofself-consistent three-dimensional N-body simulations of bar-unstabledisks are studied. Using Gauss-Hermite polynomials to describe themajor-axis stellar kinematics, a number of characteristic bar signaturesare identified in edge-on disks: (1) a major-axis light profile with aquasi-exponential central peak and a plateau at moderate radii (Freemantype II profile); (2) a ``double-hump'' rotation curve; (3) a sometimesflat central velocity dispersion peak with a plateau at moderate radiiand occasional local central minimum and secondary peak; and (4) anh3-V correlation over the projected bar length. All of thesekinematic features are spatially correlated and can easily be understoodfrom the orbital structure of barred disks. They thus provide a reliableand easy-to-use tool to identify edge-on bars. Interestingly, they areall produced without dissipation and are increasingly realized to becommon in spirals, lending support to bar-driven evolution scenarios forbulge formation. So called ``figure-of-eight'' position-velocitydiagrams are never observed, as expected for realistic orbitalconfigurations. Although not uniquely related to triaxiality,line-of-sight velocity distributions with a high-velocity tail (i.e., anh3-V correlation) appear as particularly promising tracers ofbars. The stellar kinematic features identified grow in strength as thebar evolves and vary only slightly for small inclination variations.Many can be used to trace the bar length. Comparisons with observationsare encouraging and support the view that boxy and peanut-shaped bulgesare simply thick bars viewed edge-on.
| The Advanced Camera for Surveys Virgo Cluster Survey. V. Surface Brightness Fluctuation Calibration for Giant and Dwarf Early-Type Galaxies
As part of the Advanced Camera for Surveys (ACS) Virgo Cluster Survey,we have measured surface brightness fluctuations (SBFs) in a sample of100 early-type Virgo galaxies. Distances derived from these measurementsare needed to explore the three-dimensional structure of the VirgoCluster, study the intrinsic parameters of globular clusters associatedwith the program galaxies, and compare with the galaxy distances derivedfrom globular cluster luminosity functions. Our SBF measurements havebeen performed in the F850LP bandpass of the Wide Field Channel of theACS on the Hubble Space Telescope. These are the first measurements ofthis kind, and we present the first SBF calibration for this bandpass.The measured fluctuations depend on galaxy stellar populationvariations, which we quantify by galaxy color(g475-z850)0, where g475 andz850 are the galaxy magnitudes in the F475W and F850LP ACSfilters, respectively. We derive the calibration for the absolute SBFmagnitudeM850=-2.06+/-0.04+(2.0+/-0.2)[(g475-z850)0-1.3]in the range1.3<(g475-z850)0<=1.6, andM850=-2.06+/-0.04+(0.9+/-0.2)[(g475-z850)0-1.3]in the range1.0<=(g475-z850)0<=1.3. Thequoted zero-point uncertainty here includes all sources of internalerror; there is an additional systematic uncertainty of ~0.15 mag, dueto the uncertainty in the distance scale calibration. Physically, thetwo different color regimes correspond to different galaxy types: giantellipticals and S0s at the red end, and early-type dwarfs at the blueend. For the first time in SBF studies, we are able to provide a firmempirical calibration of SBF in early-type dwarf galaxies. Our resultsagree with stellar population model predictions from Bruzual &Charlot in the range1.3<(g475-z850)0<=1.6, while ourempirical slope is somewhat steeper than the theoretical prediction inthe range 0.9<=(g475-z850)0<=1.3.
| A Chandra Snapshot Survey of Infrared-bright LINERs: A Possible Link Between Star Formation, Active Galactic Nucleus Fueling, and Mass Accretion
We present results from a high-resolution X-ray imaging study of nearbyLINERs observed by ACIS on board Chandra. This study complements andextends previous X-ray studies of LINERs, focusing on the underexploredpopulation of nearby dust-enshrouded infrared-bright LINERs. The sampleconsists of 15 IR-bright LINERs (LFIR/LB>3),with distances that range from 11 to 26 Mpc. Combining our sample withprevious Chandra studies, we find that ~51% (28/55) of the LINERsdisplay compact hard X-ray cores. The nuclear 2-10 keV luminosities ofthe galaxies in this expanded sample range from ~2×1038to ~2×1044 ergs s-1. We find that the mostextreme IR-faint LINERs are exclusively active galactic nuclei (AGNs).The fraction of LINERs containing AGNs appears to decrease with IRbrightness and increase again at the highest values ofLFIR/LB. We find that of the 24 LINERs showingcompact nuclear hard X-ray cores in the expanded sample that wereobserved at Hα wavelengths, only eight actually show evidence of abroad line. Similarly, of the 14 LINERs showing compact nuclear hardX-ray cores with corresponding radio observations, only eight display acompact flat spectrum radio core. These findings emphasize the need forhigh-resolution X-ray imaging observations in the study of IR-brightLINERs. Finally, we find an intriguing trend in the Eddington ratioversus LFIR and LFIR/LB for theAGN-LINERs in the expanded sample that extends over 7 orders ofmagnitude in L/LEdd. This correlation may imply a linkbetween black hole growth, as measured by the Eddington ratio, and thestar formation rate, as measured by the far-IR luminosity andIR-brightness ratio. If the far-IR luminosity is an indicator of themolecular gas content in our sample of LINERs, our results may furtherindicate that the mass accretion rate scales with the host galaxy's fuelsupply. We discuss the potential implications of our results in theframework of black hole growth and AGN fueling in low-luminosity AGNs.
| Multicolor Surface Photometry of Lenticular Galaxies. I. The Data
We present multicolor surface and aperture photometry in the B, V, R,and K' bands for a sample of 34 lenticular galaxies from the UppsalaGeneral Catalogue. From surface photometric analysis, we obtain radialprofiles of surface brightness, colors, ellipticity, position angle, andthe Fourier coefficients that describe the departure of isophotal shapesfrom a purely elliptical form; we find the presence of dust lanes,patches, and ringlike structure in several galaxies in the sample. Weobtain total integrated magnitudes and colors and find that these are ingood agreement with the values from the Third Reference Catalogue.Isophotal colors are correlated with each other, following the sequenceexpected for early-type galaxies. The color gradients in lenticulargalaxies are more negative than the corresponding gradients inelliptical galaxies. There is a good correlation between B-V and B-Rcolor gradients, and the mean gradients in the B-V, B-R, and V-K' colorsare -0.13+/-0.06, -0.18+/-0.06, and -0.25+/-0.11 mag dex-1 inradius, respectively.
| The ACS Virgo Cluster Survey. II. Data Reduction Procedures
The ACS Virgo Cluster Survey is a large program to carry out multicolorimaging of 100 early-type members of the Virgo Cluster using theAdvanced Camera for Surveys (ACS) on the Hubble Space Telescope. DeepF475W and F850LP images (~SDSS g and z) are being used to study thecentral regions of the program galaxies, their globular cluster systems,and the three-dimensional structure of Virgo itself. In this paper, wedescribe in detail the data reduction procedures used for the survey,including image registration, drizzling strategies, the computation ofweight images, object detection, the identification of globular clustercandidates, and the measurement of their photometric and structuralparameters.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| The ACS Virgo Cluster Survey. I. Introduction to the Survey
The Virgo Cluster is the dominant mass concentration in the LocalSupercluster and the largest collection of elliptical and lenticulargalaxies in the nearby universe. In this paper, we present anintroduction to the ACS Virgo Cluster Survey: a program to image, in theF475W and F850LP bandpasses (~Sloan g and z), 100 early-type galaxies inthe Virgo Cluster using the Advanced Camera for Surveys on the HubbleSpace Telescope. We describe the selection of the program galaxies andtheir ensemble properties, the choice of filters, the field placementand orientation, the limiting magnitudes of the survey, coordinatedparallel observations of 100 ``intergalactic'' fields with WFPC2, andsupporting ground-based spectroscopic observations of the programgalaxies. In terms of depth, spatial resolution, sample size, andhomogeneity, this represents the most comprehensive imaging survey todate of early-type galaxies in a cluster environment. We brieflydescribe the main scientific goals of the survey, which include themeasurement of luminosities, metallicities, ages, and structuralparameters for the many thousands of globular clusters associated withthese galaxies, a high-resolution isophotal analysis of galaxiesspanning a factor of ~450 in luminosity and sharing a commonenvironment, the measurement of accurate distances for the full sampleof galaxies using the method of surface brightness fluctuations, and adetermination of the three-dimensional structure of Virgo itself.ID="FN1"> 1Based on observations with the NASA/ESA Hubble SpaceTelescope obtained at the Space Telescope Science Institute, which isoperated by the association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
| Molecular Gas in Candidate Double-Barred Galaxies. III. A Lack of Molecular Gas?
Most models of double-barred galaxies suggest that a molecular gascomponent is crucial for maintaining long-lived nuclear bars. We haveundertaken a CO survey in an attempt to determine the gas content ofthese systems and to locate double-barred galaxies with strong COemission that could be candidates for high-resolution mapping. Weobserved 10 galaxies in CO J=2-1 and J=3-2 and did not detect anygalaxies that had not already been detected in previous CO surveys. Wepreferentially detect emission from galaxies containing some form ofnuclear activity. Simulations of these galaxies require that theycontain 2%-10% gas by mass in order to maintain long-lived nuclear bars.The fluxes for the galaxies for which we have detections suggest thatthe gas mass fraction is in agreement with these models requirements.The lack of emission in the other galaxies suggests that they contain aslittle as 7×106 Msolar of molecularmaterial, which corresponds to <~0.1% gas by mass. This resultcombined with the wide variety of CO distributions observed indouble-barred galaxies suggests the need for models of double-barredgalaxies that do not require a large, well-ordered molecular gascomponent.
| Stellar Kinematics of Boxy Bulges: Large-Scale Bars and Inner Disks
Long-slit stellar kinematic observations were obtained along the majoraxis of 30 edge-on spiral galaxies, 24 with a boxy or peanut-shaped(B/PS) bulge and six with other bulge types for comparison. Such B/PSbulges are identified in at least 45% of highly inclined systems, and agrowing body of theoretical and observational work suggests that theyare the edge-on projection of thickened bars. Profiles of the meanstellar velocity V, the velocity dispersion σ, as well as theasymmetric (h3) and symmetric (h4) deviations froma pure Gaussian are presented for all objects. Comparing these profileswith stellar kinematic bar diagnostics developed from N-bodysimulations, we find bar signatures in 24 of our sample galaxies (80%).Galaxies with a B/PS bulge typically show a double-humped rotation curvewith an intermediate dip or plateau. They also frequently show a ratherflat central velocity dispersion profile accompanied by a secondary peakor plateau, and numerous galaxies have a local central σ minimum(>~40%). The h3 profiles display up to three slopereversals. Most importantly, h3 is normally correlated with Vover the presumed bar length, contrary to expectations from axisymmetricdisks. These characteristic bar signatures strengthen the case for aclose relationship between B/PS bulges and bars and leave little roomfor other explanations of the bulges' shape. We also find thath3 is anticorrelated with V in the very center of mostgalaxies (>~60%), indicating that these objects additionally harborcold and dense decoupled (quasi-) axisymmetric central stellar disks,which may be related to the central light peaks. These central diskscoincide with previously identified star-forming ionized-gas disks(nuclear spirals) in gas-rich systems, and we argue that they formed outof gas accumulated by the bar at its center through inflow. As suggestedby N-body models, the asymmetry of the velocity profile (h3)appears to be a reliable tracer of asymmetries in disks, allowing us todiscriminate between axisymmetric and barred disks seen in projection.B/PS bulges (and thus a large fraction of all bulges) appear to be madeup mostly of disk material, which has acquired a large vertical extentthrough bar-driven vertical instabilities. Their formation is thusprobably dominated by secular evolution processes rather than merging.
| 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
| Properties of isolated disk galaxies
We present a new sample of northern isolated galaxies, which are definedby the physical criterion that they were not affected by other galaxiesin their evolution during the last few Gyr. To find them we used thelogarithmic ratio, f, between inner and tidal forces acting upon thecandidate galaxy by a possible perturber. The analysis of thedistribution of the f-values for the galaxies in the Coma cluster leadus to adopt the criterion f ≤ -4.5 for isolated galaxies. Thecandidates were chosen from the CfA catalog of galaxies within thevolume defined by cz ≤5000 km s-1, galactic latitudehigher than 40o and declination ≥-2.5o. Theselection of the sample, based on redshift values (when available),magnitudes and sizes of the candidate galaxies and possible perturberspresent in the same field is discussed. The final list of selectedisolated galaxies includes 203 objects from the initial 1706. The listcontains only truly isolated galaxies in the sense defined, but it is byno means complete, since all the galaxies with possible companions underthe f-criterion but with unknown redshift were discarded. We alsoselected a sample of perturbed galaxies comprised of all the diskgalaxies from the initial list with companions (with known redshift)satisfying f ≥ -2 and \Delta(cz) ≤500 km s-1; a totalof 130 objects. The statistical comparison of both samples showssignificant differences in morphology, sizes, masses, luminosities andcolor indices. Confirming previous results, we found that late spiral,Sc-type galaxies are, in particular, more frequent among isolatedgalaxies, whereas Lenticular galaxies are more abundant among perturbedgalaxies. Isolated systems appear to be smaller, less luminous and bluerthan interacting objects. We also found that bars are twice as frequentamong perturbed galaxies compared to isolated galaxies, in particularfor early Spirals and Lenticulars. The perturbed galaxies have higherLFIR/LB and Mmol/LB ratios,but the atomic gas content is similar for the two samples. The analysisof the luminosity-size and mass-luminosity relations shows similartrends for both families, the main difference being the almost totalabsence of big, bright and massive galaxies among the family of isolatedsystems, together with the almost total absence of small, faint and lowmass galaxies among the perturbed systems. All these aspects indicatethat the evolution induced by interactions with neighbors would proceedfrom late, small, faint and low mass Spirals to earlier, bigger, moreluminous and more massive spiral and lenticular galaxies, producing atthe same time a larger fraction of barred galaxies but preserving thesame relations between global parameters. The properties we found forour sample of isolated galaxies appear similar to those of high redshiftgalaxies, suggesting that the present-day isolated galaxies could bequietly evolved, unused building blocks surviving in low densityenvironments.Tables \ref{t1} and \ref{t2} are only available in electronic form athttp://www.edpsciences.org
| The origin of H I-deficiency in galaxies on the outskirts of the Virgo cluster. II. Companions and uncertainties in distances and deficiencies
The origin of the deficiency in neutral hydrogen of 13 spiral galaxieslying in the outskirts of the Virgo cluster is reassessed. If thesegalaxies have passed through the core of the cluster, their interstellargas should have been lost through ram pressure stripping by the hotX-ray emitting gas of the cluster. We analyze the positions of these HI-deficient and other spiral galaxies in velocity-distance plots, inwhich we include our compilation of velocity-distance data on 61elliptical galaxies, and compare with simulated velocity-distancediagrams obtained from cosmological N-body simulations. We find that20% relative Tully-Fisher distance errors are consistent with thegreat majority of the spirals, except for a small number of objectswhose positions in the velocity-distance diagram suggest grosslyincorrect distances, implying that the Tully-Fisher error distributionfunction has non-Gaussian wings. Moreover, we find that the distanceerrors may lead to an incorrect fitting of the Tolman-Bondi solutionthat can generate significant errors in the distance and especially themass estimates of the cluster. We suggest 4 possibilities for theoutlying H I-deficient spirals (in decreasing frequency): 1) they havelarge relative distance errors and are in fact close enough (atdistances between 12.7 and 20.9 Mpc from us) to the cluster to havepassed through its core and seen their gas removed by ram pressurestripping; 2) their gas is converted to stars by tidal interactions withother galaxies; 3) their gas is heated during recent mergers withsmaller galaxies; and 4) they are not truly H I-deficient (e.g. S0/amisclassified as Sa).Appendix A is only available in electronic form athttp://www.edpsciences.org
| Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500
| Star Formation Histories of Early-Type Galaxies. I. Higher Order Balmer Lines as Age Indicators
We have obtained blue integrated spectra of 175 nearby early-typegalaxies, covering a wide range in galaxy velocity dispersion andemphasizing those with σ<100 km s-1. Galaxies havebeen observed both in the Virgo Cluster and in lower densityenvironments. The main goals are the evaluation of higher order Balmerlines as age indicators and differences in stellar populations as afunction of mass, environment, and morphology. In this first paper, ouremphasis is on presenting the methods used to characterize the behaviorof the Balmer lines through evolutionary population synthesis models.Lower σ galaxies exhibit a substantially greater intrinsicscatter, in a variety of line-strength indicators, than do higherσ galaxies, with the large intrinsic scatter setting in below aσ of 100 km s-1. Moreover, a greater contrast inscatter is present in the Balmer lines than in the lines of metalfeatures. Evolutionary synthesis modeling of the observed spectralindexes indicates that the strong Balmer lines found primarily among thelow-σ galaxies are caused by young age, rather than by lowmetallicity. Thus we find a trend between the population age and thecentral velocity dispersion, such that low-σ galaxies have youngerluminosity-weighted mean ages. We have repeated this analysis usingseveral different Balmer lines and find consistent results from onespectral indicator to another.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| 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
| 1.65-μm (H -band) surface photometry of galaxies - VIII. The near-IR κ space at z =0
We present the distribution of a statistical sample of nearby galaxiesin the κ -space (κ 1 ~logM , κ 2~logI e 3 M /L , κ 3 ~logM /L ).Our study is based on near-IR (H -band: λ =1.65μm)observations, for the first time comprising early- and late-typesystems. Our data confirm that the mean effective dynamicalmass-to-light ratio M /L of the E+S0+S0a galaxies increases withincreasing effective dynamical mass M , as expected from the existenceof the Fundamental Plane relation. Conversely, spiral and Im/BCDgalaxies show a broad distribution in M /L with no detected trend of M/L with M , the former galaxies having M /L values about twice largerthan the latter, on average. For all the late-type galaxies, the M /Lincreases with decreasing effective surface intensity I e ,consistent with the existence of the Tully-Fisher relation. Theseresults are discussed on the basis of the assumptions behind theconstruction of the κ -space and their limitations. Our study iscomplementary to a previous investigation in the optical (B -band:λ =0.44μm) and allows us to study wavelength dependences ofthe galaxy distribution in the κ -space. As a first result, wefind that the galaxy distribution in the κ 1 -κ2 plane reproduces the transition from bulgeless tobulge-dominated systems in galaxies of increasing dynamical mass.Conversely, it appears that the M /L of late-types is higher (lower)than that of early-types with the same M in the near-IR (optical). Theorigins of this behaviour are discussed in terms of dust attenuation andstar formation history.
| A catalogue and analysis of local galaxy ages and metallicities
We have assembled a catalogue of relative ages, metallicities andabundance ratios for about 150 local galaxies in field, group andcluster environments. The galaxies span morphological types from cD andellipticals, to late-type spirals. Ages and metallicities were estimatedfrom high-quality published spectral line indices using Worthey &Ottaviani (1997) single stellar population evolutionary models. Theidentification of galaxy age as a fourth parameter in the fundamentalplane (Forbes, Ponman & Brown 1998) is confirmed by our largersample of ages. We investigate trends between age and metallicity, andwith other physical parameters of the galaxies, such as ellipticity,luminosity and kinematic anisotropy. We demonstrate the existence of agalaxy age-metallicity relation similar to that seen for local galacticdisc stars, whereby young galaxies have high metallicity, while oldgalaxies span a large range in metallicities. We also investigate theinfluence of environment and morphology on the galaxy age andmetallicity, especially the predictions made by semi-analytichierarchical clustering models (HCM). We confirm that non-clusterellipticals are indeed younger on average than cluster ellipticals aspredicted by the HCM models. However we also find a trend for the moreluminous galaxies to have a higher [Mg/Fe] ratio than the lowerluminosity galaxies, which is opposite to the expectation from HCMmodels.
| The Radio Properties of Composite LINER/H II Galaxies
Arcsecond-resolution VLA observations-newly obtained as well aspublished-of 40 nearby galaxies are discussed, completing a study of theradio properties of a magnitude-limited sample of nearby galaxies of thecomposite LINER/H II type. Our results reveal an overall detection rateof at least 25% active galactic nucleus (AGN) candidates among thesecomposite sources. The general properties of these AGN candidates, ascompared to non-AGN composite sources and H II galaxies, are discussed.
| 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.
| Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| 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.
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| Near-infrared template spectra of normal galaxies: k-corrections, galaxy models and stellar populations
We have observed 28 local galaxies in the wavelength range between 1 and2.4μm in order to define template spectra of the normal galaxiesalong the Hubble sequence. Five galaxies per morphological type wereobserved in most cases, and the resulting rms spread of the normalizedspectra of each class, including both intrinsic differences andobservational uncertainties, is about 1 per cent in K, 2 per cent in Hand 3 per cent in J. Many absorption features can be accuratelymeasured. The target galaxies and the spectroscopic aperture(7×53arcsec2) were chosen to be similar to those usedby Kinney et al. to define template UV and optical spectra. The two datasets are matched in order to build representative spectra between 0.1and 2.4μm. The continuum shape of the optical spectra and therelative normalization of the near-IR ones were set to fit the averageeffective colours of the galaxies of the various Hubble classes. Theresulting spectra are used to compute the k-corrections of the normalgalaxies in the near-IR bands, and to check the predictions of variousspectral synthesis models: while the shape of the continuum is generallywell predicted, large discrepancies are found in the absorption lines.Among the other possible applications, here we also show how thesespectra can be used to place constraints on the dominant stellarpopulation in local galaxies. Spectra and k-corrections are publiclyavailable and can be downloaded from the web site http://www.arcetri.astro.it/~filippo/spectra.
| Evidence for a massive dark object in NGC 4350
In this work we build a detailed dynamic model for an S0 galaxy possiblyhosting a central massive dark object (MDO). We show that thephotometric profiles and the kinematics along the major and minor axes,including the h3 and h4 profiles, imply thepresence of a central MDO of massMMDO~1.5-9.7×108Msolar, i.e.0.3-2.8per cent of the mass derived for the stellar spheroidalcomponent. Models without MDO are unable to reproduce the kinematicproperties of the inner stars and of the rapidly rotating nuclear gas.The stellar population consists of an exponential disc (27per cent ofthe light) and a diffuse spheroidal component (73per cent of the light)that cannot be represented by a simple de Vaucouleurs profile at anyradius. The ML ratios we found for the stellar components (3.3 and 6.6respectively) are typical of those of disc and elliptical galaxies.
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