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Lenticular Galaxies and their Environments
It is widely believed that lenticular (S0) galaxies were initiallyspirals from which the gas has been removed by interactions with hotcluster gas, or by ram pressure stripping of cool gas from spirals thatare orbiting within rich clusters of galaxies. However, problems withthis interpretation are that (1) some lenticulars, such as NGC 3115, areisolated field galaxies rather than cluster members. (2) Thedistribution of flattening values of S0 galaxies in clusters, in groups,and in the field are statistically indistinguishable. This is surprisingbecause one might have expected most of the progenitors of field S0galaxies to have been flattened late-type galaxies, whereas lenticularsin clusters are thought to have mostly been derived from bulge-dominatedearly-type galaxies. (3) It should be hardest for ram pressure to stripmassive luminous galaxies with deep potential wells. However, nostatistically significant differences are seen between the luminositydistributions of early-type Shapley-Ames galaxies in clusters, groups,and in the field. (4) Finally both ram pressure stripping andevaporation by hot intracluster gas would be most efficient in richclusters. However, the small number of available data in theShapley-Ames sample appears to show no statistically significantdifferences between the relative frequencies of dust-poor S01and dust-rich S03 galaxies in clusters, groups, and in thefield. It is tentatively concluded that ram pressure stripping andheating by intracluster gas, may not be the only evolutionary channelsthat lead to the formation of lenticular galaxies. It is speculated thatgas starvation, or gas ejection by active nuclei, may have played amajor role in the formation of a significant fraction of all S0galaxies.
| The Globular Cluster Luminosity Function and Specific Frequency in Dwarf Elliptical Galaxies
The globular cluster luminosity function, specific globular clusterfrequency, SN, specific globular cluster mass,TMP, and globular cluster mass fraction in dwarf ellipticalgalaxies are explored using the full 69 galaxy sample of the HST WFPC2Dwarf Elliptical Galaxy Snapshot Survey. The GCLFs of the dEs are wellrepresented with a t5 function with a peak atM0V,Z(dE,HST)=-7.3+/-0.1. This is ~0.3 mag fainterthan the GCLF peaks in giant spiral and elliptical galaxies, but theresults are consistent within the uncertainties. The bright-end slope ofthe luminosity distribution has a power-law form with slopeα=-1.9+/-0.1. The trend of increasing SN orTMP with decreasing host galaxy luminosity is confirmed. Themean value for TMP in dE,N galaxies is about a factor of 2higher than the mean value for nonnucleated galaxies and thedistributions of TMP in dE,N and dE,noN galaxies arestatistically different. These data are combined with results from theliterature for a wide range of galaxy types and environments. At lowhost galaxy masses the distribution of TMP for dE,noN and dIgalaxies are similar. This supports the idea that one pathway forforming dE,noN galaxies is by the stripping of dIs. The formation ofnuclei and the larger values of TMP in dE,N galaxies may bedue to higher star formation rates and star cluster formationefficiencies due to interactions in galaxy cluster environments.Based on observations with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555.
| The formation of S0 galaxies: evidence from globular clusters
Aims.We devise a simple experiment to test the theory that lenticular(S0) galaxies form from spirals whose star formation has been shut down.An individual galaxy's fading is measured using the globular clusterspecific frequency (S_N), defined as the number of globular clustersnormalised by the galaxy luminosity. This is compared with aspectroscopically-derived age estimate. Methods: We make NTT/EMMIlong-slit spectroscopic observations of 11 S0 galaxies at z < 0.006.We measure the absorption-line indices, Hδ, Hγ, Mgb, Fe5270and Fe5335 within the central r_e/8. By inverting single-stellarpopulation models, luminosity-weighted mean ages, metallicities andα-element abundance ratios are derived. We estimate the amount offading a galaxy has undergone by comparing each galaxy's SNwith its deviation from the mean spiral S_N. Results: Galaxies withhigher SN have older stellar populations. Moreover, we findthat the zero-point and amount of fading is consistent with a scenariowhere lenticulars are formed by the quenching of star formation inspiral galaxies. Our data also rule out any formation method for S0swhich creates a large number of new globular clusters. We confirm thatprevious results showing a relationship between SN and colorare driven by the SN -Age relation. Five galaxies showdetectable Hβ, [O iii], Hα or [N ii] emission lines. However,only in the two youngest galaxies is this emission unambiguously fromstar formation. Conclusions: Our results are consistent with the theorythat S0 galaxies are formed when gas in normal spirals is removed,possibly as a result of a change in environment. The on-going starformation in the youngest galaxies hints that the timescale of quenchingis ≲1 Gyr. We speculate, therefore, that the truncation of starformation is a rather gentle process unlikely to involve a rapid burstof star formation.
| Kinematics of the Local Universe. XIII. 21-cm line measurements of 452 galaxies with the Nançay radiotelescope, JHK Tully-Fisher relation, and preliminary maps of the peculiar velocity field
Aims.This paper presents 452 new 21-cm neutral hydrogen linemeasurements carried out with the FORT receiver of the meridian transitNançay radiotelescope (NRT) in the period April 2003-March 2005. Methods: This observational programme is part of a larger projectaiming at an exhaustive and magnitude-complete HI extragalacticcatalogue for Tully-Fisher applications (the so-called KLUN project, forKinematics of the Local Universe studies, to end in 2008). The wholeon-line HI archive of the NRT today contains reduced HI-profiles for4500 spiral galaxies of declination δ > -40°(http://klun.obs-nancay.fr). Results: As an example of thisapplication, we used the direct Tully-Fisher relation in three (JHK)bands in deriving distances to a large catalogue of 3126 spiral galaxiesdistributed through the whole sky and sampling the radial velocity rangewell between 0 and 8000 km s-1. Thanks to an iterative methodaccounting for selection bias and smoothing effects, we show a detailedand original map of the velocity field in the Local Universe as apreliminary output.Data Tables [see full text], [see full text], and [see full text]and HI-profiles (Fig. [see full text]) are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/465/71
| The Cool ISM in Elliptical Galaxies. I. A Survey of Molecular Gas
We present preliminary results from a survey of CO emission from membersof a volume-limited sample of non-cluster elliptical galaxies. Ourintent is to compare the gas properties of these ellipticals to a sampleof lenticulars selected using similar criteria. The data, although stillsparse, suggest that the cool gas in ellipticals shows the same puzzlingupper mass cutoff found in the lenticular galaxies. We find, however,significantly lower detection rates and possibly much lowerH2/H I mass ratios in the ellipticals. The detection rate ishigher among the lower mass galaxies, as has been found previously. Thisseems puzzling given that the deeper potential wells of the largergalaxies ought to make gas retention easier, but perhaps that effect isoverwhelmed by feedback from the central supermassive black hole. As wehave observed ~40% of our full sample, the conclusions are necessarilytentative at this time.
| Measuring the fading of S0 galaxies using globular clusters
Aims. We test the hypothesis that S0 galaxies are the descendants offading spirals whose star formation has been shut down, by using theproperties of their globular cluster systems. Methods: . Weestimate the amount by which the globular cluster specific frequency(number of globular clusters per unit V-band luminosity) is enhanced inS0s relative to spirals. If the transformation hypothesis is correct,and no clusters are created or destroyed in the process, then thisdifference provides a measure of the degree to which the S0's V-bandluminosity has faded relative to that of its spiral progenitor, which wecan compare with the independent values estimated from stellarpopulation synthesis and the S0 Tully-Fisher relation. We also explorewhether the degree to which the globular cluster specific frequency isenhanced in S0s correlates with the colour of the stellar population, asalso predicted by this hypothesis in which galaxies become redder asthey fade. Results: . We find that, on average, the globularcluster specific frequency is a factor 3 larger for S0s than forspirals, which can be interpreted as meaning that passively-evolving S0shave faded on average by about a factor of three from their spiralprogenitors. This value fits remarkably well with the predictions ofstellar population synthesis calculations, and the offset between the S0and spiral Tully-Fisher relations, where the S0 V-band relation lies 1.2 mag, or a factor of three, below the spiral relation. We alsofind that the global colours of S0 galaxies are strongly correlated withtheir globular cluster specific frequencies: the redder the stellarpopulation of an S0, the larger its specific frequency, as we mightexpect if we are catching different S0s at different stages of passivelyfading and reddening. Comparison to the predictions of stellarpopulation synthesis models show that this explanation worksquantitatively as well as qualitatively. Conclusions: . Thesetests strongly support the hypothesis that S0 galaxies were once normalspirals, whose star formation was cut off, presumably due to a change ofenvironment. We are now in a position to start to make quantitativemeasurements of when this life-changing event occurred in differentgalaxies.
| Extragalactic Globular Clusters and Galaxy Formation
Globular cluster (GC) systems have now been studied in galaxies rangingfrom dwarfs to giants and spanning the full Hubble sequence ofmorphological types. Imaging and spectroscopy with the Hubble SpaceTelescope and large ground-based telescopes have together establishedthat most galaxies have bimodal color distributions that reflect twosubpopulations of old GCs: metal-poor and metal-rich. Thecharacteristics of both subpopulations are correlated with those oftheir parent galaxies. We argue that metal-poor GCs formed in low-massdark matter halos in the early universe and that their propertiesreflect biased galaxy assembly. The metal-rich GCs were born in thesubsequent dissipational buildup of their parent galaxies and their agesand abundances indicate that most massive early-type galaxies formed thebulk of their stars at early times. Detailed studies of bothsubpopulations offer some of the strongest constraints on hierarchicalgalaxy formation that can be obtained in the near-field.
| Keck Spectroscopy of Globular Clusters in the Virgo Cluster Dwarf Elliptical Galaxy VCC 1386
We present the results of a Keck spectroscopic study of globularclusters associated with the Virgo Cluster dwarf elliptical galaxy (dE)VCC 1386. We analyze blue spectroscopic absorption lines from 3500 to5500 Å for 13 globular cluster candidates and confirm that fiveare associated with VCC 1386. By comparing metal and Balmer line indicesof these globular clusters with α-enhanced single stellarpopulation models, we find that these systems are metal poor, with[Fe/H]>-1.35, and old, with ages >5 Gyr at 3 σ confidence,placing their formation at z>~1. This is one of the firstspectroscopic studies of globular clusters surrounding dEs in a cluster,revealing that some low-mass galaxies in rich environments form at leastpart of their stellar mass early in the history of the universe. Wefurther find that the luminosity-weighted stellar population of VCC 1386itself is younger and more metal rich than its globular clusters,consistent with (V-I)0 colors from Hubble Space Telescopeimaging. This implies that VCC 1386, like the Local Group dEs, has hadmultiple episodes of star formation. Globular clusters associated withlow-luminosity systems, however, appear to be roughly as old as thoseassociated with giant galaxies, contrary to the ``downsizing'' formationof their bulk stellar populations.
| The Globular Cluster System of the Virgo Dwarf Elliptical Galaxy VCC 1087
We present an analysis of the globular cluster (GC) system of thenucleated dwarf elliptical galaxy VCC 1087 in the Virgo Cluster based onKeck LRIS spectroscopy and archival Hubble Space Telescope AdvancedCamera for Surveys imaging. We estimate that VCC 1087 hosts a totalpopulation of 77+/-19 GCs, which corresponds to a relatively high V-bandspecific frequency of 5.8+/-1.4. The g475-z850color distribution of the GCs shows a blue (metal-poor) peak with a tailof redder (metal-rich) clusters similar in color to those seen inluminous elliptical galaxies. The luminosity function of the GCs islognormal and peaks atMTOg475=-7.2+/-0.3,MTOz850=-8.1+/-0.2. These peakpositions are consistent with those found for luminous Virgo ellipticalgalaxies, suggesting either the lack of or, surprisingly similarly, thedynamical destruction processes of GCs among dwarf and giant galaxies.Spectroscopy of a subsample of 12 GCs suggests that the GC system is oldand coeval (>~10 Gyr), with a fairly broad metallicity distribution(-1.8<~[M/H]<~-0.8). In contrast, an integrated spectrum of theunderlying galaxy starlight reveals that its optical luminosity isdominated by metal-rich, intermediate-age stars. The radial velocitiesof the GCs suggest rotation close to the major axis of the galaxy, andthis rotation is dynamically significant with(vrot/σlos)*>1. A compilationof the kinematics of the GC systems of nine early-type galaxies showssurprising diversity in the (vrot/σlos)parameter for GC systems. In this context, the GC system of VCC 1087exhibits the most significant rotation-to-velocity dispersion signature.Dynamical mass modeling of the velocity dispersion profile of the GCsand galaxy stars suggests fairly constant mass-to-light ratios of ~3 outto 6.5 kpc. The present observations can entertain both baryonic andnonbaryonic solutions, and GC velocities at larger radii would be mostvaluable with regard to this issue. Finally, we discuss the evolution ofVCC 1087 in terms of the galaxy ``harassment'' scenario and concludethat this galaxy may well be the remains of a faded, tidally perturbedSc spiral.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.
| Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters
We present new (B, I) photometry for the globular cluster systems ineight brightest cluster galaxies (BCGs), obtained with the ACS/WFCcamera on the Hubble Space Telescope. In the very rich cluster systemsthat reside within these giant galaxies, we find that all have stronglybimodal color distributions that are clearly resolved by themetallicity-sensitive (B-I) index. Furthermore, the mean colors andinternal color range of the blue subpopulation are remarkably similarfrom one galaxy to the next, to well within the +/-0.02-0.03 maguncertainties in the foreground reddenings and photometric zero points.By contrast, the mean color and internal color range for the redsubpopulation differ from one galaxy to the next by twice as much as theblue population. All the BCGs show population gradients, with muchhigher relative numbers of red clusters within 5 kpc of their centers,consistent with their having formed at later times than the blue,metal-poor population. A striking new feature of the color distributionsemerging from our data is that for the brightest clusters(MI<-10.5) the color distribution becomes broad and lessobviously bimodal. This effect was first noticed by Ostrov et al. andDirsch et al. for the Fornax giant NGC 1399; our data suggest that itmay be a characteristic of many BCGs and perhaps other large galaxies.Our data indicate that the blue (metal-poor) clusters brighter thanMI~=-10 become progressively redder with increasingluminosity, following a mass/metallicity scaling relationZ~M0.55. A basically similar relation has been found for M87by Strader et al. (2005). We argue that these GCS characteristics areconsistent with a hierarchical-merging galaxy formation picture in whichthe metal-poor clusters formed in protogalactic clouds or densestarburst complexes with gas masses in the range107-1010 Msolar, but where the moremassive clusters on average formed in bigger clouds with deeperpotential wells where more preenrichment could occur.
| The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei, and Stellar Halos
We present the results of a Hubble Space Telescope WFPC2 F555W and F814Wsurvey of 69 dwarf elliptical galaxies (dEs) in the Virgo and FornaxClusters and Leo Group. The V-I colors of the dE globular clusters,nuclei, and underlying field-star populations are used to trace the dEstar formation histories. We find that the dE globular clustercandidates are as blue as the metal-poor globular clusters of the MilkyWay. The observed correlation of the dE globular cluster systems' V-Icolor with the luminosity of the host dE is strong evidence that theglobular clusters were formed within the halos of dEs and do not have apregalactic origin. Assuming that the majority of dE clusters are old,the mean globular cluster color-host galaxy luminosity correlationimplies a cluster metallicity-galaxy luminosity relation of~L0.22+/-0.05B, which issignificantly shallower than the field-star metallicity-host galaxyluminosity relationship observed in Local Group dwarfs(~L0.4). The dE stellar envelopes are0.1-0.2 mag redder in V-I than their globular clusters and nuclei. Thiscolor offset implies separate star formation episodes within the dEs forthe clusters and field stars, while the very blue colors of two dEnuclei trace a third star formation event in those dEs less than 1 Gyrago.
| A Catalog of Neighboring Galaxies
We present an all-sky catalog of 451 nearby galaxies, each having anindividual distance estimate D<~10 Mpc or a radial velocityVLG<550 km s-1. The catalog contains data onbasic optical and H I properties of the galaxies, in particular, theirdiameters, absolute magnitudes, morphological types, circumnuclearregion types, optical and H I surface brightnesses, rotationalvelocities, and indicative mass-to-luminosity and H I mass-to-luminosityratios, as well as a so-called tidal index, which quantifies the galaxyenvironment. We expect the catalog completeness to be roughly 70%-80%within 8 Mpc. About 85% of the Local Volume population are dwarf (dIr,dIm, and dSph) galaxies with MB>-17.0, which contributeabout 4% to the local luminosity density, and roughly 10%-15% to thelocal H I mass density. The H I mass-to-luminosity and the H Imass-to-total (indicative) mass ratios increase systematically fromgiant galaxies toward dwarfs, reaching maximum values about 5 in solarunits for the most tiny objects. For the Local Volume disklike galaxies,their H I masses and angular momentum follow Zasov's linear relation,expected for rotating gaseous disks being near the threshold ofgravitational instability, favorable for active star formation. We foundthat the mean local luminosity density exceeds 1.7-2.0 times the globaldensity, in spite of the presence of the Tully void and the absence ofrich clusters in the Local Volume. The mean local H I density is 1.4times its ``global'' value derived from the H I Parkes Sky Survey.However, the mean local baryon densityΩb(<8Mpc)=2.3% consists of only a half of the globalbaryon density, Ωb=(4.7+/-0.6)% (Spergel et al.,published in 2003). The mean-square pairwise difference of radialvelocities is about 100 km s-1 for spatial separations within1 Mpc, increasing to ~300 km s-1 on a scale of ~3 Mpc. alsoWe calculated the integral area of the sky occupied by the neighboringgalaxies. Assuming the H I size of spiral and irregular galaxies to be2.5 times their standard optical diameter and ignoring any evolutioneffect, we obtain the expected number of the line-of-sight intersectionswith the H I galaxy images to be dn/dz~0.4, which does not contradictthe observed number of absorptions in QSO spectra.
| 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.
| Globular cluster candidates within the Fornax Cluster: Intracluster globulars?
We present the results of a search for globular clusters in thesurroundings of 15 low surface brightness dwarf galaxies belonging tothe Fornax Cluster, which was carried out on CCD images obtained withthe C and T_1 filters of the Washington photometric system. The globularcluster candidates show an extended and probably bimodal (C-T_1) colordistribution, which is inconsistent with the presence of a singlepopulation of metal-poor clusters detected in several dwarf galaxies.The surface number density of these candidates shows no concentrationtowards the respective dwarf galaxies, in whose outskirts they have beenidentified. On the contrary, if we split the candidates in two groupsaccording to their projected distances to the center of the FornaxCluster, those located closer to the center show a higher projecteddensity than those located farther from it. These results suggest thatthe potential globular clusters might not be bound to the dwarfgalaxies. Alternatively, these globulars could form part of the veryperipheral regions of NGC 1399 (the central galaxy ofthe Fornax Cluster) or even belong to the intracluster medium.Based on observations obtained at Cerro Tololo Inter-AmericanObservatory, NOAO, which is operated by AURA, Inc., under cooperativeagreement with the National Science Foundation.
| New Members of the Cluster Family in Nearby Lenticular Galaxies
Using spectra obtained with the Keck I Telescope, we have demonstratedconclusively that the faint (23<=V<=24 mag) and unusually extendedobjects we discovered in Hubble Space Telescope images of the lenticulargalaxies NGC 1023 and NGC 3384 are star clusters associated with theirrespective galaxies. In the case of NGC 1023, we were further able toestablish that these objects are old (>=7-8 Gyr) and moderatelymetal-rich ([Fe/H]=-0.58+/-0.24) and, having a system rotation curvethat is very similar to that of the host galaxy, are associated with thelenticular disk. The ?-element to iron abundance ratios are highlysupersolar with [?/Fe] between +0.3 and +0.6. With moderately highmetallicities and luminosities and effective radii in the range 7-15 pc(compared with the 2-3 pc sizes typical of normal globular and openclusters), this population of clusters has no known analog in the MilkyWay or elsewhere in the Local Group. Based on data obtained at the W. M.Keck Observatory, which is operated as a scientific partnership amongthe California Institute of Technology, the University of California,and the National Aeronautics and Space Administration. The Observatorywas made possible by the generous financial support of the W. M. KeckFoundation.
| Structure and stellar content of dwarf galaxies. VII. B and R photometry of 25 southern field dwarfs and a disk parameter analysis of the complete sample of nearby irregulars
We present B and R band surface photometry of 25 Southern field dwarfgalaxies within a distance of 10 Mpc. For each galaxy we give theessential model-free photometric parameters and, by fitting exponentialsto the surface brightness profiles, the central extrapolated surfacebrightness and the exponential scale length, in both colour bands.Surface brightness and colour profiles are shown. One of the objects, avery faint dwarf elliptical in the vicinity of NGC 2784, has beendiscovered in the course of this work. Drawing on the data from this andall previous papers of this series, we construct a complete sample of 72late-type (``irregular'') dwarf galaxies in nearby groups and the fieldwithin the 10 Mpc volume, to study the exponential-disk parameterrelations of these galaxies with respect to galaxy environment. Weconfirm our previous finding of statistically lower scale lengths/highercentral surface brightnesses for field and group galaxies as compared tocluster galaxies. However, using a clear-cut definition of ``group''versus ``field'' environment, we find no significant difference in thephotometric structure of group and field irregulars. A difference in thestar formation history may partly account for this structure-environmentrelation: for a given luminosity cluster dwarfs are on average redderthan field and group galaxies. We also report evidence for the colourgradients of dwarf irregulars being roughly inversely proportional tothe disk scale lengths. Supplementing our photometric data withkinematic data from the literature, we study possible relations withkinematic properties of the inner disk. Applying the dark matter scalingrelations for a Burkert halo we show that for field and group galaxiesof a given luminosity faster-than-mean disk rotational velocities at aradius of about two scale lengths are correlated with larger-than-meandisk scale lengths. Based on observations collected at the EuropeanSouthern Observatory, La Silla, Chile. Table 3 containing ``BRphotometry and kinematic data for the 72 irregular dwarf galaxies of ourcomplete sample'' is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/388/29
| HI observations of nearby galaxies. IV. More dwarf galaxies in the southern sky
In this paper we present HI observations of nearby galaxies from twomore lists of the Karachentsev catalog of candidates for nearby dwarfgalaxies in the southern sky. Observations north of declination -31degrwere performed with the 100-m radio telescope at Effelsberg. Data formore southern galaxies were taken from HIPASS(www.atnf.csiro.au/research/multibeam). This sample is a supplement tothe list of 94 southern dwarf galaxy candidates (1998, A&AS, 127,409) located in the same declination range around the known Local Volumegalaxies (i.e. galaxies within 10 Mpc, LV hereafter). We observed 17galaxies not observed in the previous sample; and all 67 candidate dwarfgalaxies from the SERC EJ sky survey (Karachentsev et al.\cite{Karachentsev00) and 81 objects from a supplementary list ofcandidate dwarf galaxies (Karachentseva & Karachentsev\cite{Karachentseva00}). This yields a total of 165 (=17 + 67 + 81)galaxies. Overall we have a detection rate of 48%. The sample ofdetected galaxies has the following median parameters: radial velocityVLG= 1127 km s-1, HI line width W50 =59 km s-1, absolute blue magnitude MBT0= -14.4 mag, linear diameter A0 = 4.0 kpc, hydrogenmass-to-luminosity ratio 1.6 Msun/Lsun. The sampleof known galaxies within the Local Volume increased from 179 in 1979(Kraan-Korteweg & Tammann \cite{KraanKorteweg79}) to 387 now. Thiscorresponds to an increase in total luminosity of 22%. The known HI massin the LV increased by 25%; the relative HI contentMHI/LB increased from 0.21 to 0.26 for the wholevolume. However we still might have missed half of the dwarf galaxies inthe Local Volume. Table 1 is also, and Table 2 only, available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(139.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/377/801
| New Insights from Hubble Space Telescope Studies of Globular Cluster Systems. II. Analysis of 29 S0 Systems
We examine the globular cluster systems (GCSs) of a sample of 34 S0galaxies from a WFPC2 snapshot survey in the V and I bands. Of these 34galaxies, 29 have measurable globular cluster systems. The mean color ofthe GCSs of individual galaxies vary from V-I=0.85 mag to V-I=1.17 mag.The average color of GCSs in all 29 S0 galaxies, V-I=1.00+/-0.07 mag, issimilar to the value of V-I=1.04+/-0.04 derived for ellipticals in acompanion paper. The mean metallicity of a cluster system is correlatedto the luminosity (or mass) of the host galaxy, but it is not dependenton the Hubble type. Our measurements of the local specific frequency, onthe other hand, confirm that the cluster formation efficiency is afunction of Hubble type. The mean local specific frequency of our samplewithin the WFPC2 field of view is 1.0+/-0.6, lower thanSN(Local)=2.4+/-1.8 derived for ellipticals in a similaranalysis. Although we are able to confirm a bimodal color distributionin only one galaxy from the shallow ``snapshot'' images analyzed in thispaper, statistical tests suggest that 10%-20% of S0s are bimodal at thepresent level of photometric accuracy. There are no significant trendsin GCS properties with membership or location of the S0 host in a galaxycluster. We have measured the turnover luminosity of the globularcluster luminosity function (GCLF) for the richest few GCSs and find theGCLF distances to be in agreement with other estimates. The globularclusters in S0 galaxies have average half-light radii of ~2.6 pc, whichis similar to that of other galaxies, including our own. Based onobservations with the NASA/ESA Hubble Space Telescope, obtained at theSpace Telescope Science Institute, which is operated by the Associationof Universities for Research in Astronomy (AURA), Inc., under NASAcontract NAS 5-26555.
| Globular Cluster Systems. II. On the Formation of Old Globular Clusters and Their Sites of Formation
We studied the metal-poor globular cluster populations of a largevariety of galaxies and compared their mean metallicity with theproperties of the host galaxies. For this purpose, we constructed acomprehensive database of old metal-poor globular cluster populations,hosted by 47 galaxies, spanning about 10 mag in absolute brightness. Themean metallicities of the systems are found to be very similar and liein the -1.65<[Fe/H]<=-1.20 range (74% of the population). Usingonly globular cluster systems with more than six objects detected, wefind that 85% of the population are within -1.65<[Fe/H]<=-1.20.The relation between the mean metallicity of the metal-poor globularcluster systems and the absolute V magnitude of their host galaxiespresents a very low slope that includes zero. An analysis of thecorrelation of the mean metallicity of the populations with other galaxyproperties (such as velocity dispersion, metallicity, and environmentdensity) also leads to the conclusion that no strong correlation exists.The lack of correlation with galaxy properties suggests a formation ofall metal-poor globular clusters in very similar gas fragments. A weakcorrelation (to be confirmed) might exist between the mean metallicityof the metal-poor clusters and the host galaxy metallicity. This wouldimply that at least some fragments in which metal-poor globular clustersformed were already embedded in the larger dark matter halo of the finalgalaxy (as opposed to being independent satellites that were accretedlater). Our result suggests a homogeneous formation of metal-poorglobular clusters in all galaxies in typical fragments of masses around109-1010 Msolar with very similarmetallicities, compatible with hierarchical formation scenarios forgalaxies. We further compare the mean metallicities of the metal-poorglobular cluster populations with the typical metallicities ofhigh-redshift objects. If we add the constraint that globular clustersneed a high column density of gas to form, damped Lyα systems arethe most likely sites among the known high-redshift objects for theformation of metal-poor globular cluster populations.
| The Colors of Globular Clusters
A compilation has been made of available data on the ratio of the numberof metal-rich ([Fe/H]>-1.0) to metal-poor ([Fe/H]<-1.0) clustersin various globular cluster systems. Among early-type galaxies of typesE, E/S0, and S0, the ratio of blue to red globular clusters is found tovary by almost 2 orders of magnitude. The data suggest that cD galaxieshave the widest range of evolutionary histories. The fraction ofmetal-rich red clusters is largest among early-type galaxies and appearsto decrease toward later Hubble types.
| Local Field of Galaxy Velocities
A sample of 145 galaxies having radial velocities relative to thecentroid of the Local Group V LG D H ij , with principal values of81:62:48 in km/sec·Mpc, which have a standard error of 4km/sec·Mpc. The minor axis of the Hubble ellipsoid is orientedalmost along the polar axis of the Local Supercluster, while the majoraxis forms an angle = (29 ± 5)° with the direction toward thecenter of the Virgo Cluster. Such a configuration of thepeculiar-velocity field shows unsatisfactory agreement with the model ofa spherically symmetric flow of galaxies toward the Virgo Cluster.Rotation of the Local Supercluster may be one reason for thisdifference. The peculiar velocities of galaxies within a volume with D V= 74 km/sec, a considerable part of which is due to the virial motionsof galaxies in groups and to distance errors. For field galaxies,located in a layer of 1 < D < 3 Mpc around the Local Group, theradial-velocity dispersion does not exceed 25 km/sec. Thevelocitydistance relation, constructed from the 20 closestgalaxies around the Local Group with D < 3 Mpc and with errorsσ(D) < 0.2 Mpc, exhibits the expected effect of gravitationaldeceleration. Using the estimate of R 0 = (0.96 ± 0.05) Mpc forthe observed radius of the zero-velocity sphere, we determined the totalmass of the Local Group to be (1.2 ± 0.2)·1012 M ȯ,which agrees well with the sum of the virial masses of the subgroups ofgalaxies around the Local Group and M31. The ratio of the Local Group'stotal mass (within R 0) to its luminosity is M/L = (23 ± 4) Mȯ/L ȯ, which does not require the existence of supermassivedark halos around our Galaxy and M31.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| Dwarf galaxy candidates found on the SERC EJ sky survey
We inspected a sky region with declination range of [0degr , -18degr ]based on the SERC EJ plate copies. As a result a list of 50 nearby dwarfgalaxy candidates with angular diameters >= 0farcm5 is presented.Most of the galaxies have low and very low surface brightness. More than60% of the objects are detected for the first time.
| Globular Clusters in the DE,N Galaxy NGC 3115 DW1: New Insights from Spectroscopy and Hubble Space Telescope Photometry
The properties of globular clusters in dwarf galaxies are key tounderstanding the formation of globular cluster systems and inparticular in verifying scenarios in which globular cluster systems oflarger galaxies formed (at least partly) from the accretion of dwarfgalaxies. Here, we revisit the globular cluster system of the dE,Ngalaxy NGC 3115 DW1-a companion of the nearby S0 galaxy NGC 3115-addingKeck/LRIS spectroscopy and Hubble Space Telescope (HST) Wide FieldPlanetary Camera 2 imaging to previous ground-based photometry. Spectrafor seven globular clusters reveal normal abundance ratios with respectto the Milky Way and M31 clusters, as well as a relatively high meanmetallicity ([Fe/H]~-1.0+/-0.1 dex). Crude kinematics indicate a highvelocity dispersion within 10 kpc that could be caused either by darkmatter-dominated outer regions or by the stripping of outer globularclusters by the nearby giant galaxy NGC 3115. The total galaxy mass outto 3 and 10 kpc lies between 1×1010 and1×1011 Msolar and 2×1010and 4×1011 Msolar, respectively, dependingon the mass estimator used and the assumptions on cluster orbits andsystemic velocity. The HST imaging allows measurement of sizes for twoclusters, returning core radii around 2.0 pc, similar to the sizesobserved in other galaxies. Spectroscopy allows an estimate of thedegree of contamination by foreground stars or background galaxies forthe previous ground-based photometry but does not require a revision ofprevious results: NGC 3115 DW1 hosts around NGC=60+/-20clusters, which corresponds to a specific frequency ofSN=4.9+/-1.9, on the high end for massive dE's. Given itsabsolute magnitude (MV=-17.7 mag) and the properties of itscluster system, NGC 3115 DW1 appears to be a transition between aluminous dE and low-luminosity E galaxy.
| Some Musings on Globular Cluster Systems
Globular cluster systems exhibit a bewildering variety ofcharacteristics. No single scenario appears to be able to account forthe wide range of specific globular cluster frequencies that areobserved in galaxies of various types. The fraction of all starformation that produces massive bound clusters differs from galaxy togalaxy and (in some cases) appears to vary with time. Currentlyavailable data strongly suggest that the specific cluster formingfrequency is highest during violent bursts of star formation. Globularcluster systems show a wide variety of color (metallicity)distributions, with many luminous galaxies having double (or evenmultiple) metallicity peaks that were probably produced during distinctepisodes of cluster formation. The bulk of the globulars in the mainbody of the Galactic halo appear to have formed during a singleshort-lived burst that took place ~13 Gyr ago. This was followed by asecond, perhaps more extended, burst associated with the formation ofthe Galactic bulge. A few metal-rich clusters may also be associatedwith the formation of the Galactic thick disk. Finally, many of theclusters beyond RGc~=15 kpc might have been formed in dwarfspheroidal galaxies that, after a few Gyr, were accreted by the mainbody of the Galactic halo. Some of these outer clusters are younger, andless luminous, than the majority of globular clusters formed at smallerGalactocentric distances.
| A Database of Cepheid Distance Moduli and Tip of the Red Giant Branch, Globular Cluster Luminosity Function, Planetary Nebula Luminosity Function, and Surface Brightness Fluctuation Data Useful for Distance Determinations
We present a compilation of Cepheid distance moduli and data for foursecondary distance indicators that employ stars in the old stellarpopulations: the planetary nebula luminosity function (PNLF), theglobular cluster luminosity function (GCLF), the tip of the red giantbranch (TRGB), and the surface brightness fluctuation (SBF) method. Thedatabase includes all data published as of 1999 July 15. The mainstrength of this compilation resides in the fact that all data are on aconsistent and homogeneous system: all Cepheid distances are derivedusing the same calibration of the period-luminosity relation, thetreatment of errors is consistent for all indicators, and measurementsthat are not considered reliable are excluded. As such, the database isideal for comparing any of the distance indicators considered, or forderiving a Cepheid calibration to any secondary distance indicator, suchas the Tully-Fisher relation, the Type Ia supernovae, or the fundamentalplane for elliptical galaxies. This task has already been undertaken byFerrarese et al., Sakai et al., Kelson et al., and Gibson et al.Specifically, the database includes (1) Cepheid distances, extinctions,and metallicities; (2) reddened apparent λ5007 Å magnitudesof the PNLF cutoff; (3) reddened apparent magnitudes and colors of theturnover of the GCLF (in both the V and B bands); (4) reddened apparentmagnitudes of the TRGB (in the I band) and V-I colors at 0.5 mag fainterthan the TRGB; and (5) reddened apparent surface brightness fluctuationmagnitudes measured in Kron-Cousin I, K', andKshort, and using the F814W filter with the Hubble SpaceTelescope (HST) WFPC2. In addition, for every galaxy in the database wegive reddening estimates from IRAS/DIRBE as well as H I maps, J2000coordinates, Hubble and T-type morphological classification, apparenttotal magnitude in B, and systemic velocity.
| The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXVI. The Calibration of Population II Secondary Distance Indicators and the Value of the Hubble Constant
A Cepheid-based calibration is derived for four distance indicators thatutilize stars in old stellar populations: the tip of the red giantbranch (TRGB), the planetary nebula luminosity function (PNLF), theglobular cluster luminosity function (GCLF), and the surface brightnessfluctuation method (SBF). The calibration is largely based on theCepheid distances to 18 spiral galaxies within cz=1500 km s-1obtained as part of the Hubble Space Telescope (HST) Key Project on theExtragalactic Distance Scale, but relies also on Cepheid distances fromseparate HST and ground-based efforts. The newly derived calibration ofthe SBF method is applied to obtain distances to four Abell clusters inthe velocity range 3800-5000 km s-1. Combined with clustervelocities corrected for a cosmological flow model, these distancesimply a value of the Hubble constant of H0=69+/-4(random)+/-6 (systematic) km s-1 Mpc-1. Thisresult assumes that the Cepheid PL relation is independent of themetallicity of the variable stars; adopting a metallicity correction asin Kennicutt et al. would produce a 5%+/-3% decrease in H0.Finally, the newly derived calibration allows us to investigatesystematics in the Cepheid, PNLF, SBF, GCLF, and TRGB distance scales.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| HI properties of nearby galaxies from a volume-limited sample
We consider global HI and optical properties of about three hundrednearby galaxies with V_0 < 500 km s(-1) . The majority of them haveindividual photometric distance estimates. The galaxy sample parametersshow some known and some new correlations implying a meaningful dynamicexplanation: 1) In the whole range of diameters, 1 - 40 Kpc, the galaxystandard diameter and rotational velocity follows a nearly linearTully-Fisher relation, lg A25~(0.99+/-0.06)lg V_m. 2) The HImass-to-luminosity ratio and the HI mass-to-``total" mass (inside thestandard optical diameter) ratio increase systematically from giantgalaxies towards dwarfs, reaching maximum values 5 ;M_ȯ/L_ȯand 3, respectively. 3) For all the Local Volume galaxies their totalmass-to-luminosity ratio lies within a range of [0.2-16]M_ȯ/L_ȯ with a median of 3.0 ;M_ȯ/L_ȯ. TheM25/L ratio decreases slightly from giant towards dwarfgalaxies. 4) The M_HI/L and M25/L ratios for the samplegalaxies correlate with their mean optical surface brightness, which maybe caused by star formation activity in the galaxies. 5) The M_HI/L andM25/L ratios are practically independent of the local massdensity of surrounding galaxies within the range of densities of aboutsix orders of magnitude. 6) For the LV galaxies their HI mass andangular momentum follow a nearly linear relation: lgM_HI~(0.99+/-0.04)lg (V_m* A25), expected for rotatinggaseous disks being near the threshold of gravitational instability,favourable for active star formation. Table in the Appendix is availableonly in electronic form at the CDS via anonymous ftp 130.79.128.5 orhttp//cdsweb.u-strasbg.fr/Abstract.html
| The Globular Cluster System of the dE,N Galaxy NGC 3115 DW1
Globular clusters in dwarf galaxies are of interest in two respects. Onthe one hand, they might provide information on the star formationhistory of these galaxies. On the other hand, they are a key toscenarios in which a large fraction of the globular cluster systems ofgiant ellipticals are built up by the accretion of satellites. Werevisit the globular cluster system of the bright (M_V -17.7) dE,Ngalaxy NGC 3115 DW1, now adding low-resolution spectra of 46 globularcluster candidates to the previous photometric study. The spectra wereobtained with LRIS on the Keck II telescope. From their spectralfeatures and their radial velocities, we identified 5 globular clusters,17 foreground stars, and 8 background galaxies (which are significantlyclumped in redshift). 16 remaining objects are unclassified because oftheir too low spectral S/N ratio. Thus, we confirm, at most, 50% of theglobular cluster candidates previously identified from photometry.Taking the extreme cases - namely that the 16 unclassified objects areall fore- or background objects, or that all are indeed globularclusters - results in the following revisions of the total number ofclusters (N_GC) and specific frequency (S_N). N_GC=14+/- 5 andS_N=1.17+/- 0.5 in the first case, and N_GC=28+/- 11 and S_N=2.3+/- 0.9in the second case. In either case, the values are now in good agreementwith those observed in low-luminosity field ellipticals. A kinematicalanalysis of our data gives a lower limit for the mass of NGC 3115 DW1 ofM_gal 9? 1010M_odot. Lick absorption line indices aremeasured for the 5 globular clusters and metallicities are derived.
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