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Massive Star Cluster Populations in Irregular Galaxies as Probable Younger Counterparts of Old Metal-rich Globular Cluster Populations in Spheroids
Peak metallicities of metal-rich populations of globular clusters(MRGCs) belonging to early-type galaxies and spheroidal subsystems ofspiral galaxies (spheroids) of different mass fall within the somewhatconservative -0.7<=[Fe/H]<=-0.3 range. Indeed, if possible ageeffects are taken into account, this metallicity range might becomesmaller. Irregular galaxies such as the Large Magellanic Cloud (LMC),with longer timescales of formation and lower star formation (SF)efficiency, do not contain old MRGCs with [Fe/H]>-1.0, but they areobserved to form populations of young/intermediate-age massive starclusters (MSCs) with masses exceeding 104 Msolar.Their formation is widely believed to be an accidental process fullydependent on external factors. From the analysis of available data onthe populations and their hosts, including intermediate-age populousstar clusters in the LMC, we find that their most probable meanmetallicities fall within -0.7<=[Fe/H]<=-0.3, as the peakmetallicities of MRGCs do, irrespective of signs of interaction.Moreover, both the disk giant metallicity distribution function (MDF) inthe LMC and the MDFs for old giants in the halos of massive spheroidsexhibit a significant increase toward [Fe/H]~-0.5. That is in agreementwith a correlation found between SF activity in galaxies and theirmetallicity. The formation of both the old MRGCs in spheroids and MSCpopulations in irregular galaxies probably occurs at approximately thesame stage of the host galaxies' chemical evolution and is related tothe essentially increased SF activity in the hosts around the samemetallicity that is achieved very early in massive spheroids, later inlower mass spheroids, and much later in irregular galaxies. Changes inthe interstellar dust, particularly in elemental abundances in dustgrains and in the mass distribution function of the grains, may be amongthe factors regulating star and MSC formation activity in galaxies.Strong interactions and mergers affecting the MSC formation presumablyplay an additional role, although they can substantially intensify theinternally regulated MSC formation process. Several implications of oursuggestions are briefly discussed.
| Stellar populations of early-type galaxies in different environments. III. Line-strength gradients
Aims.This is the third paper of a series devoted to the study of thestellar content of early-type galaxies. The goal of the series is to setconstraints on the evolutionary status of these objects. Methods:.We present line-strength gradients for 22 spectral indices measured ina sample of 82 early-type galaxies in different environments, includingthe high-density cores of the Coma cluster, the Virgo cluster, poorgroups, and isolated field galaxies. Using new evolutionary populationsynthesis models, we derive age and metallicity gradients, and comparethe mean values with the predictions of different galaxy formationmodels. We explore the behaviour of individual chemical species byderiving the metallicity gradient with different indicators.Results: .We find that the strength of the metallicity gradient inferredfrom stellar population models depends on the specific Lick indexemployed. In particular, metallicity gradients obtained with CN2 andC4668 combined with Hβ are steeper than those measured using Ca4227or Fe4383. The correlation of the metallicity gradients with otherparameters also depends on the specific index employed. If themetallicity gradient is obtained using CN2 and Mgb, then it correlateswith the central age of the galaxies. On the contrary, if Fe4383 orCa4227 is used, the metallicity gradient correlates with the velocitydispersion gradient. Conclusions: .This may suggest that severalmechanisms have helped to set the age and metallicity gradients inearly-type galaxies. While we do not find any correlation between themetallicity gradient and the central velocity dispersion for galaxies inlow-density environments, we find a marginal correlation between themetallicity gradient and the mass for galaxies in the centre of the Comacluster. We also find a trend for which galaxies in denser environmentsshow a steeper metallicity gradient than galaxies in less denseenvironments. We interpret these results in light of the differentmechanisms proposed to explain the observed changes between galaxies asa function of environment.
| Stellar populations of early-type galaxies in different environments. II. Ages and metallicities
Aims.This is the second paper of a series devoted to the study of thestellar content of early-type galaxies. The goal of the series is to setconstraints on the evolutionary status of these objects Methods:.We use a new set of models that include an improved stellar library(MILES) to derive simple stellar population (SSP)-equivalent parametersin a sample of 98 early-type galaxies. The sample contains galaxies inthe field, poor groups, and galaxies in the Virgo and Coma clusters. Results: .We find that low-density environment galaxies span a largerrange in SSP age and metallicity than their counterparts in high densityenvironments, with a tendency for lower σ galaxies to be younger.Early-type galaxies in low-density environments appear on average ~1.5Gyr younger and more metal rich than their counterparts in high densityenvironments. The sample of low-density environment galaxies shows anage-metallicity relation in which younger galaxies are found to be moremetal rich, but only when metallicity is measured with a Fe-sensitiveindex. Conversely, there is no age-metallicity relation when themetallicity is measured with a Mg sensitive index. The mass-metallicityrelation is only appreciable for the low-density environment galaxieswhen the metallicity is measured with a Mg-sensitive index, and not whenthe metallicity is measured with other indicators. On the contrary, thisrelation exists for the high-density environment galaxies independent ofthe indicator used to measure the metallicity. Conclusions: .Thissuggests a dependence of the mass-metallicity relation on theenvironment of the galaxies. Our data favour a scenario in whichgalaxies in low density environments have suffered a more extended starformation history than the galaxies in the Coma cluster, which appear tohost more homogenous stellar populations.
| Stellar populations of early-type galaxies in different environments. I. Line-strength indices. Relations of line-strengths with σ
Aims.This paper commences a series devoted to the study of the stellarcontent of early-type galaxies. The goal of the series is to setconstraints on the evolutionary status of these objects. Methods:.In this paper we describe the details of the galaxy sample, theobservations, and the data reduction. Line-strength indices and velocitydispersions (σ) are measured in 98 early-type galaxies drawn fromdifferent environments, and the relation of the indices with thevelocity dispersion analysed in detail. Results: .The presentsample indicates that some of the index-σ relations depend ongalaxy environment. In particular, the slope of the relation betweenBalmer lines and σ is steeper for galaxies in the Virgo cluster,small groups, and in the field than for galaxies in the Coma cluster. Inseveral indices there is also a significant offset in the zero pointbetween the relations defined by the different subsamples. The slopes ofthe index-σ relation for the Virgo and low-density environmentgalaxies are explained by a variation of both age and metallicity, withvelocity dispersion, as previously noted in other studies. For thegalaxies in the Coma cluster, however, the relation of the indices withσ only requires a variation of the abundance along the σsequence. In agreement with other studies, we find that the models thatbetter reproduce the slopes are those in which the α elements varymore than the Fe-peak elements along the σ sequence, while, at agiven σ, older galaxies show an higher α/Fe ratio. Conclusions: .The results can be explained assuming that galaxies in theComa cluster have experienced a truncated star formation and chemicalenrichment history compared to a more continuous time-extended historyfor their counterparts in lower density environments.
| The Epochs of Early-Type Galaxy Formation as a Function of Environment
The aim of this paper is to set constraints on the epochs of early-typegalaxy formation through the ``archaeology'' of the stellar populationsin local galaxies. Using our models of absorption-line indices thataccount for variable abundance ratios, we derive ages, totalmetallicities, and element ratios of 124 early-type galaxies in high-and low-density environments. The data are analyzed by comparison withmock galaxy samples created through Monte Carlo simulations taking thetypical average observational errors into account, in order to eliminateartifacts caused by correlated errors. We find that all threeparameters, age, metallicity, and α/Fe ratio, are correlated withvelocity dispersion. We show that these results are robust againstrecent revisions of the local abundance pattern at high metallicities.To recover the observed scatter we need to assume an intrinsic scatterof about 20% in age, 0.08 dex in [Z/H], and 0.05 dex in [α/Fe].All low-mass objects withM*<~1010Msolar (σ<~130kms-1) show evidence for the presence of intermediate-agestellar populations with low α/Fe ratios. About 20% of theintermediate-mass objects with1010<~M*/Msolar<~1011[110<~σ/(kms-1)<~230 both elliptical andlenticular galaxies] must have either a young subpopulation or a bluehorizontal branch. On the basis of the above relationships, valid forthe bulk of the sample, we show that the Mg-σ relation is mainlydriven by metallicity, with similar contributions from the α/Feratio (23%) and age (17%). We further find evidence for an influence ofthe environment on the stellar population properties. Massive early-typegalaxies in low-density environments seem on average ~2 Gyr younger andslightly (~0.05-0.1 dex) more metal-rich than their counterparts inhigh-density environments. No offsets in the α/Fe ratios areinstead detected. With the aid of a simple chemical evolution model, wetranslate the derived ages and α/Fe ratios into star formationhistories. We show that most star formation activity in early-typegalaxies is expected to have happened between redshifts ~3 and 5 inhigh-density environments and between redshifts 1 and 2 in low-densityenvironments. We conclude that at least 50% of the total stellar massdensity must have already formed at z~1, in good agreement withobservational estimates of the total stellar mass density as a functionof redshift. Our results suggest that significant mass growth in theearly-type galaxy population below z~1 must be restricted to lessmassive objects, and a significant increase of the stellar mass densitybetween redshifts 1 and 2 should be present, caused mainly by the fieldgalaxy population. The results of this paper further imply the presenceof vigorous star formation episodes in massive objects at z~2-5 andevolved elliptical galaxies around z~1, both observationally identifiedas SCUBA galaxies and extremely red objects, respectively.
| Active and Star-forming Galaxies and Their Supernovae
To investigate the extent to which nuclear starbursts or other nuclearactivity may be connected with enhanced star formation activity in thehost galaxy, we perform a statistical investigation of supernovae (SNe)discovered in host galaxies from four samples: the Markarian galaxiessample, the Second Byurakan Survey (SBS) sample, the north Galactic pole(NGP) sample of active or star-forming galaxies, and the NGP sample ofnormal galaxies. Forty-seven SNe in 41 Mrk galaxies, 10 SNe in six SBSgalaxies, 29 SNe in 26 NGP active or star-forming galaxies, and 29 SNein 26 NGP normal galaxies have been studied. We find that the rate ofSNe, particularly core-collapse (Types Ib/c and II) SNe, is higher inactive or star-forming galaxies in comparison with normal galaxies.Active or star-forming host galaxies of SNe are generally of latermorphological type and have lower luminosity and smaller linear sizethan normal host galaxies of SNe. The radial distribution of SNe inactive and star-forming galaxies shows a higher concentration toward thecenter of the active host galaxy than is the case for normal hostgalaxies, and this effect is more pronounced for core-collapse SNe.Ib/c-type SNe have been discovered only in active and star-forminggalaxies of our samples. About 78% of these SNe are associated with H IIregions or are located very close to the nuclear regions of these activegalaxies, which are in turn hosting AGNs or starburst nuclei. Besidesthese new results, our study also supports the conclusions of severalother earlier papers. We find that Type Ia SNe occur in all galaxytypes, whereas core-collapse SNe of Types Ib/c and II are found only inspiral and irregular galaxies. The radial distribution of Type Ib SNe intheir host galaxies is more centrally concentrated than that of Type IIand Ia SNe. The radial distances of Types Ib/c and II SNe, from thenuclei of their host galaxies, is larger for barred spiral hosts.Core-collapse SNe are concentrated in spiral arms and are often close toor in the H II regions, whereas Type Ia SNe show only a looseassociation with spiral arms and no clear association with H II regions.
| Extragalactic globular clusters in the near-infrared. V. IC 4051 and NGC 3311
We present the results of combined optical and near-infrared photometryfor the globular cluster systems of the giant ellipticals IC 4051 andNGC 3311. We use the reduced age-metallicity degeneracy in (V-I) vs.(V-H) color-color diagrams to derive the cumulative age distributionwithin the red sub-population of globular clusters and to search for agesub-populations. The age distribution is then compared to the onedetermined for simulated globular cluster systems in order to setconstraints on the relative age and size of these globular clustersub-populations. In both galaxies we find a significant fraction ofglobular clusters with ages between 2-5 Gyr. We also investigate themetallicity distribution in both systems. Small number statisticsprevent us from making any definite statements concerning NGC 3311, butwe find that the derived metallicity distribution of the IC 4051clusters strongly depends on the assumed age distribution. Based on ourmost likely result that finds a large number of young/intermediate ageclusters (~2 Gyr) within the selected globular cluster sample, we findmetallicity peaks at ~-0.2 for the old clusters and +0.8 for the youngclusters. Only few very metal poor clusters are found. However, themetallicity distribution within the young/intermediate globular clusterpopulation is significantly affected by our choice of the applied SingleStellar Population model. The mean metallicity of the second generationof globular clusters changes from the above mentioned and extremely high+0.8 dex to +0.2 dex. Note that the model dependency becomes less severewith an increasing age of the cluster population.
| The Group Evolution Multiwavelength Study (GEMS): bimodal luminosity functions in galaxy groups
We present B- and R-band luminosity functions (LFs) for a sample of 25nearby groups of galaxies. We find that the LFs of the groups with lowX-ray luminosity (LX < 1041.7 ergs-1) are significantly different from those of the X-raybrighter groups, showing a prominent dip around MB=-18. Whileboth categories show lack of late-type galaxies in their centralregions, X-ray dim groups also show a more marked concentration ofoptical luminosity towards the centre. A toy simulation shows that inthe low velocity dispersion environment, as in the X-ray dim group,dynamical friction would facilitate more rapid merging, thus depletingintermediate-luminosity galaxies to form a few giant central galaxies,resulting in the prominent dip seen in our LFs. We suggest that X-raydim (or low velocity dispersion) groups are the present sites of rapiddynamical evolution rather than their X-ray bright counterparts, and maybe the modern precursors of fossil groups. We predict that these groupsof low velocity dispersion would harbour younger stellar populationsthan groups or clusters with higher velocity dispersion.
| Nuclear stellar discs in low-luminosity elliptical galaxies: NGC 4458 and 4478
We present the detection of nuclear stellar discs in the low-luminosityelliptical galaxies, NGC 4458 and 4478, which are known to host akinematically decoupled core. Using archival Hubble Space Telescopeimaging, and available absorption line-strength index data based onground-based spectroscopy, we investigate the photometric parameters andthe properties of the stellar populations of these central structures.Their scalelength, h, and face-on central surface brightness,μc0, fit on the μc0-hrelation for galaxy discs. For NGC 4458, these parameters are typicalfor nuclear discs, while the same quantities for NGC 4478 lie betweenthose of nuclear discs and the discs of discy ellipticals. We presentLick/Image Dissector Scanner (IDS) absorption line-strength measurementsof Hβ, Mgb and along the major and minor axes of thegalaxies. We model these data with simple stellar populations thataccount for the α/Fe overabundance. The counter-rotating centraldisc of NGC 4458 is found to have similar properties to the decoupledcores of bright ellipticals. This galaxy has been found to be uniformlyold despite being counter-rotating. In contrast, the cold central discof NGC 4478 is younger, richer in metals and less overabundant than themain body of the galaxy. This points to a prolonged star formationhistory, typical of an undisturbed disc-like, gas-rich (possiblypre-enriched) structure.
| Quantitative Morphology of Galaxies in the Core of the Coma Cluster
We present a quantitative morphological analysis of 187 galaxies in aregion covering the central 0.28 deg2 of the Coma Cluster.Structural parameters from the best-fitting Sérsicr1/n bulge plus, where appropriate, exponential disk model,are tabulated here. This sample is complete down to a magnitude of R=17mag. By examining the recent compilation by Edwards et al. of galaxyredshifts in the direction of Coma, we find that 163 of the 187 galaxiesare Coma Cluster members and that the rest are foreground and backgroundobjects. For the Coma Cluster members, we have studied differences inthe structural and kinematic properties between early- and late-typegalaxies and between the dwarf and giant galaxies. Analysis of theelliptical galaxies reveals correlations among the structural parameterssimilar to those previously found in the Virgo and Fornax Clusters.Comparing the structural properties of the Coma Cluster disk galaxieswith disk galaxies in the field, we find evidence for an environmentaldependence: the scale lengths of the disk galaxies in Coma are 30%smaller. An analysis of the kinematics shows marginal differencesbetween the velocity distributions of elliptical galaxies withSérsic index n<2 (dwarfs) and those with n>2 (giants), thedwarf galaxies having a greater (cluster) velocity dispersion. Finally,our analysis of all 421 background galaxies in the catalog of Edwards etal. reveals a nonuniform distribution in redshift with contrasts indensity of ~3, characterized by a void extending from ~10,000 to ~20,000km s-1, and two dense and extended structures centered at~20,000 and ~47,000 km s-1.
| The Globular Cluster System of NGC 1399. II. Kinematics of a Large Sample of Globular Clusters
We study the kinematics and dynamics of the globular cluster system ofNGC 1399, the brightest elliptical galaxy near the center of the Fornaxcluster of galaxies. The observational data consists ofmedium-resolution spectra, obtained at the Very Large Telescope withFORS2 and the Mask Exchange Unit (MXU). Our sample comprises 468 radialvelocities in the magnitude range 201.6) and blue clusters (C-R<1.6), and find velocitydispersions for these groups of 255+/-13 and 291+/-14 km s-1,respectively, again radially constant. Any possible rotation of eitherof these cluster populations is below the detection limit, with theexception of a weak signature of rotation for the blue clusters moredistant than 6'. Spherical models point to a circular velocity of419+/-30 km s-1, assuming isotropy for the red clusters. Thisvalue is constant out to 40 kpc. The inferred dark halo potential can bewell represented by a logarithmic potential. A halo of the NFW type alsoprovides a good fit to the observations. The orbital structure of theclusters can only be weakly constrained. It is consistent with isotropyfor the red clusters and a slight tangential bias for the blue clusters.Some mass profiles derived from X-ray analyses do not agree with aconstant circular velocity within our radial range, irrespective of itsexact value. Interpreting the extreme low radial velocities as spacevelocities of bound clusters near their pericentric distances wouldrequire an extension of the cluster system of at least 200 kpc.Implications for formation scenarios of the cluster system are brieflycommented on.Based on observations collected at the European Southern Observatory,Cerro Paranal, Chile; ESO program 66.B-0393.
| The X-ray luminosity function of galaxies in the Coma cluster
The XMM-Newton survey of the Coma cluster of galaxies covers an area of1.86 square degrees with a mosaic of 16 pointings and has a total usefulintegration time of 400 ks. Detected X-ray sources with extent less than10'' were correlated with cataloged galaxies in the Comacluster region. The redshift information, which is abundant in thisregion of the sky, allowed us to separate cluster members frombackground and foreground galaxies. For the background sources, werecover a typical Log N-Log S in the flux range10-15-10-13 ergs s-1 cm-2 inthe 0.5-2.0 keV band. The X-ray emission from the cluster galaxiesexhibits X-ray colors typical of thermal emission. The luminosities ofComa galaxies lie in the 1039-1041 ergss-1 interval in the 0.5-2.0 keV band. The luminosity functionof Coma galaxies reveals that their X-ray activity is suppressed withrespect to the field by a factor of 5.6, indicating a lower level ofX-ray emission for a given stellar mass.
| The impact of high pressure cluster environment on the X-ray luminosity of Coma early-type galaxies
We present an observational study of the LX vs. LBσ2 relation for early-type galaxies in the Coma clusterbased on the XMM-Newton survey data. Compared to a similar relation fora sample dominated by field early-type galaxies, the Coma clustergalaxies show a flatter slope. Our calculations show that adiabaticcompression produces a flattening in the LX vs.LBσ2 relation that is in remarkableagreement with the observed effect. Our scenario is further supported bythe observed compactness of the X-ray emission of Coma galaxies.
| Intergalactic Globular Clusters and the Faint End of the Galaxy Number Counts in A1656 (Coma)
The existence of an intergalactic globular cluster population in theComa cluster of galaxies has been tested using surface brightnessfluctuations. The main result is that the intergalactic globular clustersurface density (NIGC) does not correlate with the distanceto the center of Coma and hence with the environment. Furthermore,comparing these results with different Coma mass distribution modelpredictions, it is suggested that NIGC must in fact be zeroall over Coma. On the other hand, the results for NIGC andthe faint end of the galaxy number counts (beyond mR=23.5)are connected. So NIGC=0 settles the slope of this function,which turns out to be γ=0.36+/-0.01 down to mR=26.5.The fact that NIGC=0 all over Coma suggests that globularclusters were formed only, or almost only, from protogalactic clouds.None, or perhaps very few, could have formed in isolated regions. Italso seems inappropriate to advocate a relationship betweenintergalactic globular clusters and dark matter distributions, althoughit is true that the relationship could still exist but not be strongenough to have been detected. Finally, since our conclusion is thatintergalactic globular clusters do not exist in Coma, accretion ofintergalactic globular clusters might not be significant in galaxyformation and evolutionary processes in the Coma galaxies.
| 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.
| Spatially resolved spectroscopy of Coma cluster early-type galaxies. III. The stellar population gradients
Based on Paper I of this series (Mehlert et al. \cite{Mehlert00}), wederive central values and logarithmic gradients for the Hβ, Mg andFe indices of 35 early-type galaxies in the Coma cluster. We find thatpure elliptical galaxies have on average slightly higher velocitydispersions, lower Hβ, and higher metallic line-strengths thangalaxies with disks (S0). The latter form two families, one comparableto the ellipticals and a second one with significantly higher Hβ,and weaker metallic lines. Our measured logarithmic gradients within theeffective radius are ~ -0.037, ~ -0.029, ~ +0.017 and ~ -0.063. The gradients strongly correlate with the gradientsof sigma , but only weakly with the central index values and galaxyvelocity dispersion. Using stellar population models with variableelement abundance ratios from Thomas et al. (\cite{Thomas03a}) we deriveaverage ages, metallicities and [α/Fe] ratios in the center and atthe effective radius. We find that the α/Fe ratio correlates withvelocity dispersion and drives 30% of the Mg-sigma relation, theremaining 70% being caused by metallicity variations. We confirmprevious findings that part of the lenticular galaxies in the Comacluster host very young ( ~ 2 Gyr) stellar populations, hence must haveexperienced relatively recent star formation episodes. Again inaccordance with previous work we derive negative metallicity gradients (~ -0.16 dex per decade) that are significantly flatter than what isexpected from gaseous monolithic collapse models, pointing to theimportance of mergers in the galaxy formation history. Moreover, themetallicity gradients correlate with the velocity dispersion gradients,confirming empirically earlier suggestions that the metallicity gradientin ellipticals is produced by the local potential well. The gradients inage are negligible, implying that no significant residual star formationhas occurred either in the center or in the outer parts of the galaxies,and that the stellar populations at different radii must have formed ata common epoch. For the first time we derive the gradients of theα/Fe ratio and find them very small on average. Hence, α/Feenhancement is not restricted to galaxy centers but it is a globalphenomenon. Our results imply that the Mg-sigma local relation inside agalaxy, unlike the global Mg-sigma relation, must be primarily drivenby metallicity variations alone. Finally we note that none of thestellar population parameters or their gradients depend on the densityprofile of the Coma cluster, even though it spans 3 dex in density.Appendix A (Tables A.1-A.3) is only available in electronic form athttp://www.edpsciences.org
| 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
| Stellar populations in early-type Coma cluster galaxies - I. The data
We present a homogeneous and high signal-to-noise ratio data set (meanS/N ratio of ~60 Å-1) of Lick/IDS stellar populationline indices and central velocity dispersions for a sample of 132 bright(bj<= 18.0) galaxies within the central 1°(≡1.26h-1 Mpc) of the nearby rich Coma cluster (A1656). Ourobservations include 73 per cent (100 out of 137) of the totalearly-type galaxy population (bj<= 18.0). Observationswere made with the William Herschel 4.2-m telescope and theAUTOFIB2/WYFFOS multi-object spectroscopy instrument (resolution of~2.2-Å FWHM) using 2.7-arcsec diameter fibres (≡0.94h-1 kpc). The data in this paper have well-characterizederrors, calculated in a rigorous and statistical way. Data are comparedwith previous studies and are demonstrated to be of high quality andwell calibrated on to the Lick/IDS system. Our data have median errorsof ~0.1 Å for atomic line indices, ~0.008 mag for molecular lineindices and 0.015 dex for velocity dispersions. This work provides awell-defined, high-quality baseline at z~ 0 for studies of medium- tohigh-redshift clusters. Subsequent papers will use this data set toprobe the stellar populations (which act as fossil records of galaxyformation and evolution) and the spectrophotometric relations of thebright early-type galaxies within the core of the Coma cluster.
| 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.
| New clues to the evolution of dwarf early-type galaxies
Surface photometry of 18 Virgo cluster dwarf elliptical (dE) and dwarflenticular (dS0) galaxies, made by Gavazzi et al. in the H band(1.65μm) and in the B band (0.44μm), shows that the ratio of theeffective radii of these stellar systems in the B and H bands, r eB /r eH , ranges between 0.7 and 2.2. In particular,dwarf ellipticals and lenticulars with a red total colour index B -H(i.e. with 3.2
| 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.
| Globular Cluster Specific Frequencies in Coma
Globular cluster systems (GCSs) have been observed in 17 ellipticalgalaxies located in Coma. Surface brightness fluctuations (SBF) and a2.5-m ground-based telescope (INT, La Palma) have been used to determinetotal populations of Globular clusters (GCs) and specific frequency(SN) has been evaluated for each individual galaxy.
| Dissecting the Luminosity Function of the Coma Cluster of Galaxies Using Canada-France-Hawaii Telescope Wide-Field Images
We determined the relative spatial density of the Coma Cluster galaxies,selected by luminosity and by central brightness, i.e., the luminosityfunction bivariate in central brightness. The Coma Cluster and controlfields were imaged using the CFH12K(42'×28') and UH8K(28'×28') wide-field cameras at theCanada-France-Hawaii Telescope. Selected Hubble Space Telescope (HST)images were used for testing. Quantities were derived from measurementsin at least two colors, which have the following features: (1) galaxiesas faint as 3 times the luminosity of the brightest globular clustersare in the completeness region of our data. (2) We have a completecensus (in the explored region) of low surface brightness galaxies witha central surface brightness almost as low as the faintest ones so farcataloged. (3) The explored area is among the largest ever sampled withCCDs at comparable depth for any cluster of galaxies. (4) The errorbudget includes all sources of errors known to date. Using HST images,we also discovered that blends of globular clusters, not resolved intoindividual components due to seeing, look like dwarf galaxies whenobserved from the ground and are numerous and bright. When mistaken asextended sources, they increase the steepness of the luminosity functionat faint magnitudes. The derived Coma luminosity function is relativelysteep (α=-1.4) over the 11 magnitudes sampled, but the slope andshape depend on color. A large population of faint low surfacebrightness galaxies was discovered, representing the largest contributor(in number) to the luminosity function at faint magnitudes. We found aclear progression for a faintening of the luminosity function from highsurface brightness galaxies (μ~20 mag arcsec-2) togalaxies of very faint central brightness (μ~24.5 magarcsec-2), and some evidence for a steepening. Compactgalaxies, usually classified as stars and therefore not included in theluminosity function, are found to be a minor population in Coma. Basedon observations obtained at the Canada-France-Hawaii Telescope and inpart at the Hubble Space Telescope.
| Globular Cluster Systems in Elliptical Galaxies of Coma
Globular cluster systems of 17 elliptical galaxies have been studied inthe Coma Cluster of galaxies. Surface-brightness fluctuations have beenused to determine total populations of globular clusters, and specificfrequency (SN) has been evaluated for each individual galaxy.Enormous differences in SN between similar galaxies arefound. In particular, SN results vary by an order ofmagnitude from galaxy to galaxy. Extreme cases are the following: (1) atthe lower end of the range, NGC 4673 has SN=1.0+/-0.4, asurprising value for an elliptical galaxy, but typical for spiral andirregular galaxies; (2) at the upper extreme, MCG +5-31-063 hasSN=13.0+/-4.2 and IC 4051 has SN=12.7+/-3.2, andthey are more likely to belong to supergiant cD galaxies than to``normal'' elliptical galaxies. Furthermore, NGC 4874, the centralsupergiant cD galaxy of the Coma Cluster, also exhibits a relativelyhigh specific frequency (SN=9.0+/-2.2). The other galaxiesstudied have SN in the range [2, 7], the mean value beingSN=5.1. No single scenario seems to account for the observedspecific frequencies, so the history of each galaxy must be deducedindividually by suitably combining the different models (in situ,mergers, and accretions). The possibility that Coma is formed by severalsubgroups is also considered. If only the galaxies of the main subgroupdefined by Gurzadyan & Mazure are used, a trend in SNarises in the sense of SN being bigger in higher-densityregions. This result needs further confirmation.
| Globular Cluster Systems in Four Brightest Cluster Galaxies: A262, A3560, A3565, and A3742
We have used deep I-band (F814W) images from the Hubble Space Telescopearchive to study the globular cluster systems around the brightestcluster galaxies (BCGs) in A262, A3560, A3565, and A3742. Three of theseBCGs have inner dust lanes and peculiar structural features thatindicate past histories of low-level interaction and accretion. The deepI-band WFPC2 images have photometric limits that, for all four galaxies,reach near or just beyond the globular cluster luminosity function(GCLF) turnover point. Their specific frequencies are 8.24+/-1.65,4.66+/-0.93, 2.58+/-0.52, and 2.62+/-0.52, respectively, all within afactor of 2 of the normal range for giant elliptical galaxies. We obtainnew estimates of the GCLF turnover magnitudes, which are shown to beconsistent with an adopted Hubble constant of H0~=70 kms-1 Mpc-1 on the ``Hubble diagram'' of GCLFturnover apparent magnitude versus redshift, on a distance scale wherethe fundamental GCLF calibrator E galaxies (M87 and others) in Virgo areat d=16 Mpc. Based 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. These observations are associatedwith proposal ID 5910.
| 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.
| The far-ultraviolet emission of early-type galaxies
We have assembled a UV-flux selected sample of 82 early-type galaxiesand collected additional information at other wavelengths. These dataconfirm a large spread of the UV-V color in the range 2 to 5. The spreadin UV-V is accompanied by a spread in B-V that is mainly attributed tothe range of morphological types and luminosities. A large fraction ofthe objects have red colors, UV-V = 4 +/- 0.4, corresponding to a weakUV-upturn as observed with IUE. If the current interpretation for the UVemission from early-type galaxies is applicable to our sample, the PAGB(Post-Asymptotic Giant Branch) tracks are the most common evolution pathfor the low-mass stars responsible for the UV emission. A small numberof very blue (UV-V < 1.4) objects have been found that can bereasonably interpreted as harbouring some low level of star formation.In contrast to a previous sample based on IUE observations, nocorrelation is found between the UV-V color and the Mg2spectral line index; possible explanations are reviewed. The potentialof a more extended UV survey like GALEX is briefly presented.
| 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.
| Cold gas in elliptical galaxies
We explore the evolution of the cold gas (molecular and neutralhydrogen) of elliptical galaxies and merger remnants ordered into a timesequence on the basis of spectroscopic age estimates. We find that thefraction of cold gas in early merger remnants decreases significantlyfor ~1-2Gyr, but subsequent evolution toward evolved elliptical systemssees very little change. This trend can be attributed to an initial gasdepletion by strong star formation, which subsequently declines toquiescent rates. This explanation is consistent with the merger picturefor the formation of elliptical galaxies. We also explore the relationbetween the HI-to-H2 mass ratio and spectroscopic galaxy age,but find no evidence for a statistically significant trend. Thissuggests little net HI-to-H2 conversion for the systems inthe present sample.
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