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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.
| Study of the Structure of the Coma Cluster Based on a Hierarchical Force Clustering Method
Six subclusters in the Coma cluster have been selected on the basis of ahierarchical clustering method that takes the gravitational interactionamong galaxies into account. Of these, 3 central subclusters around thegalaxies NGC 4889, NGC 4874, and NGC 4839 have been singled out. We haveused the objective statistical criterion applied by Vennik and Anosovain studies of close groups of galaxies to evaluate each member includedin a subcluster with a high probability. Galaxies with a significantdeficit of hydrogen HI, including objects from the Bravo-Alfaro list,have been identified with members of the subclusters, with the greatestnumber of them in the subclusters around NGC 4874 and NGC 4839. Aquantitative estimate of the hydrogen deficit using the HI index in theRCG3 catalog reveals a statistically significant excess value for thosegalaxies that are members of the subclusters compared to galaxies with ahydrogen deficit in the overall Coma cluster field. A substantial numberof the spiral galaxies with a hydrogen deficit in the subclusters turnedout to be radio galaxies as well.
| 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.
| 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
| 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.
| 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.
| 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.
| 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.
| Structural evolution in elliptical galaxies: the age-shape relation
We test the hypothesis that the apparent axial ratio of an ellipticalgalaxy is correlated with the age of its stellar population. We findthat old ellipticals (with estimated ages t>7.5Gyr) are rounder onaverage than younger ellipticals. The statistical significance of thisshape difference is greatest at small radii; a Kolmogorov-Smirnov testcomparing the axial ratios of the two populations at R=Re/16yields a statistical significance greater than 99.96 per cent. Therelation between age and apparent shape is linked to the core/power-lawsurface brightness profile dichotomy. Core ellipticals have olderstellar populations, on average, than power-law ellipticals and arerounder in their inner regions. Our findings are consistent with ascenario in which power-law ellipticals are formed in gas-rich mergers,while core ellipticals form in dissipationless mergers, with coresformed and maintained by the influence of a binary black hole.
| On the dependence of spectroscopic indices of early-type galaxies on age, metallicity and velocity dispersion
We investigate the Mg-σ and -σ relations in asample of 72 early-type galaxies drawn mostly from cluster and groupenvironments using a homogeneous data set which is well calibrated on tothe Lick/IDS system. The small intrinsic scatter in Mg at a givenσ gives upper limits on the spread in age and metallicity of 49and 32 per cent respectively, if the spread is attributed to onequantity only, and if the variations in age and metallicity areuncorrelated. The age/metallicity distribution as inferred from theHβ versus diagnostic diagram reinforces this conclusion,as we find mostly galaxies with large luminosity-weighted ages spanninga range in metallicity. Using Monte Carlo simulations, we show that thegalaxy distribution in the Hβ versus plane cannot bereproduced by a model in which galaxy age is the only parameter drivingthe index-σ relation. In our sample we do not find significantevidence for an anticorrelation of ages and metallicities which wouldkeep the index-σ relations tight while hiding a large spread inage and metallicity. As a result of correlated errors in theage-metallicity plane, a mild age-metallicity anticorrelation cannot becompletely ruled out by the current data. Correcting the line-strengthindices for non-solar abundance ratios, following the recent paper byTrager et al., leads to higher mean metallicity and slightly younger ageestimates while preserving the metallicity sequence. The [Mg/Fe] ratiois mildly correlated with the central velocity dispersion, and rangesfrom [Mg/Fe]=0.05 to 0.3 for galaxies withσ>100kms-1. Under the assumption that there is noage gradient along the index-σ relations, theabundance-ratio-corrected Mg-σ, Fe-σ and Hβ-σrelations give consistent estimates ofΔ[M/H]/Δlogσ~=0.9+/-0.1. The slope of theHβ-σ relation limits a potential age trend as a function ofσ to 2-3Gyr along the sequence.
| A Photometric and Spectroscopic Study of Dwarf and Giant Galaxies in the Coma Cluster. II. Spectroscopic Observations
This is the second paper in a series studying the photometric andspectroscopic properties of galaxies of different luminosities in theComa Cluster. We present the sample selection, spectroscopicobservations, and completeness functions. To study the spectralproperties of galaxies as a function of their local environment, twofields were selected for spectroscopic observations to cover both thecore (Coma 1) and outskirts (i.e., southwest of the core and centered onNGC 4839; Coma 3) of the cluster. To maximize the efficiency ofspectroscopic observations, two subsamples were defined, consisting of``bright'' and ``faint'' galaxies, both drawn from magnitude-limitedparent samples. Medium-resolution spectroscopy (6-9 Å) was thencarried out for a total of 490 galaxies in both fields (302 in Coma 1and 188 in Coma 3), using the WYFFOS multifiber spectrograph on theWilliam Herschel Telescope. The galaxies cover a range of 122. The completeness functions for our sampleare calculated. These show that the bright sample is 65% complete atR<17 mag, becoming increasingly incomplete toward fainter magnitudes,while the faint sample follows a monotonically decreasing completenessfunction at R>19 mag. Based on observations made with the WilliamHerschel Telescope, operated on the island of La Palma by the IsaacNewton Group in the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.
| Luminosity versus Phase-Space-Density Relation of Galaxies Revisited
We reexamined the correlation between the BTmagnitude and the phase-space-density parameterw=(D225vc)-1 of galaxies forthe Virgo, the Coma, the Fornax, and the Perseus clusters in an effortto better understand the physical underpinning of the fundamental plane.A tight correlation (BT=alog w+b) common to differentmorphological types of galaxies (E, S0, S) was found for the Virgo andthe Coma clusters, with a=1.87+/-0.10 and 1.33+/-0.11, respectively. Aninvestigation using only E galaxies was made for the four clusters. Theresults indicated that the empirical linear relation might be commonamong the Coma, the Fornax, and the Perseus clusters, with the VirgoCluster showing deviation. This relation, which is another way toproject the fundamental plane, has an expression insensitive to themorphology and may be suitable for treating galaxies of differentmorphological types collectively.
| 1.65 μm (H-band) surface photometry of galaxies. III. observations of 558 galaxies with the TIRGO 1.5 m telescope
We present near-infrared H-band (1.65 μm ) surface photometry of 558galaxies in the Coma Supercluster and in the Virgo cluster. This dataset, obtained with the Arcetri NICMOS3 camera ARNICA mounted on theGornergrat Infrared Telescope, is aimed at complementing, withobservations of mostly early-type objects, our NIR survey of spiralgalaxies in these regions, presented in previous papers of this series.Magnitudes at the optical radius, total magnitudes, isophotal radii andlight concentration indices are derived. We confirm the existence of apositive correlation between the near-infrared concentration index andthe galaxy H-band luminosity Based on observations taken at TIRGO(Gornergrat, Switzerland). TIRGO is operated by CAISMI-CNR, Arcetri,Firenze, Italy. Tables 1 and 2 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Spatially resolved spectroscopy of Coma cluster early-type galaxies. I. The database
We present long slit spectra for a magnitude limited sample of 35 E andS0 galaxies of the Coma cluster. The high quality of the data allowed usto derive spatially resolved spectra for a substantial sample of Comagalaxies for the first time. From these spectra we obtained rotationcurves, the velocity dispersion profiles and the H_3 and H_4coefficients of the Hermite decomposition of the line of sight velocitydistribution. Moreover, we derive the radial line index profiles of Mg,Fe and Hβ line indices out to R~ 1 r_e - 3 r_e with highsignal-to-noise ratio. We describe the galaxy sample, the observationsand data reduction, and present the spectroscopic database. Ground-basedphotometry for a subsample of 8 galaxies is also presented. The Comacluster is one of the richest known clusters of galaxies, spanning about4 decades in density. Hence it is the ideal place to study the structureof galaxies as a function of environmental density in order to constrainthe theories of galaxy formation and evolution. Based on thespectroscopic database presented, we will discuss these issues in aseries of future papers. Tables 1 and 4 are also available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/Abstract.html Tables 5 to 82 are onlyavailable in electronic form at CDS.
| Extensive near-infrared (H-band) photometry in Coma
We present extensive and accurate photometry in the near-infrared H bandof a complete sample of objects in an area of about 400arcmin2 toward the Coma cluster of galaxies. The sample,including about 300 objects, is complete down to H ~ 17 mag, the exactvalue depending on the type of magnitude (isophotal, aperture, Kron) andthe particular region studied. This is six magnitudes below thecharacteristic magnitude of galaxies, well into the dwarfs' regime atthe distance of the Coma cluster. For each object (star or galaxy) weprovide aperture magnitudes computed within five different apertures,the magnitude within the 22 mag arcsec-2 isophote, the Kronmagnitude and radius, magnitude errors, as well as the coordinates, theisophotal area, and a stellarity index. Photometric errors are 0.2 magat the completness limit. This sample is meant to be the zero-redshiftreference for evolutionary studies of galaxies. Based on observationscollected with the Telescope Bernard Lyot, at the Pic du MidiObservatory, operated by INSU (CNRS).
| 1.65 μm (H-band) surface photometry of galaxies. V. Profile decomposition of 1157 galaxies
We present near-infrared H-band (1.65 μm) surface brightness profiledecomposition for 1157 galaxies in five nearby clusters of galaxies:Coma, A1367, Virgo, A262 and Cancer, and in the bridge between Coma andA1367 in the ``Great Wall". The optically selected (mpg≤16.0) sample is representative of all Hubble types, from E to Irr+BCD,except dE and of significantly different environments, spanning fromisolated regions to rich clusters of galaxies. We model the surfacebrightness profiles with a de Vaucouleurs r1/4 law (dV), withan exponential disk law (E), or with a combination of the two (B+D).From the fitted quantities we derive the H band effective surfacebrightness (μe) and radius (re) of each component, theasymptotic magnitude HT and the light concentration indexC31. We find that: i) Less than 50% of the Ellipticalgalaxies have pure dV profiles. The majority of E to Sb galaxies is bestrepresented by a B+D profile. All Scd to BCD galaxies have pureexponential profiles. ii) The type of decomposition is a strong functionof the total H band luminosity (mass), independent of the Hubbleclassification: the fraction of pure exponential decompositionsdecreases with increasing luminosity, that of B+D increases withluminosity. Pure dV profiles are absent in the low luminosity rangeLH<1010 L\odot and become dominantabove 1011 L\odot . Based on observations taken atTIRGO, Gornergrat, Switzerland (operated by CAISMI-CNR, Arcetri,Firenze, Italy) and at the Calar Alto Observatory (operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy). Table 2 and Figs. 2, 3, 4are available in their entirety only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening
Accurate maps of Galactic reddening are important for a number ofapplications, such as mapping the peculiar velocity field in the nearbyuniverse. Of particular concern are systematic errors which vary slowlyas a function of position on the sky, as these would induce spuriousbulk flow. We have compared the reddenings of Burstein & Heiles (BH)and those of Schlegel, Finkbeiner, & Davis (SFD) to independentestimates of the reddening, for Galactic latitudes |b|>10^deg. Ourprimary source of Galactic reddening estimates comes from comparing thedifference between the observed B-V colors of early-type galaxies, andthe predicted B-V color determined from the B-V-Mg_2 relation. We havefitted a dipole to the residuals in order to look for large-scalesystematic deviations. There is marginal evidence for a dipolar residualin the comparison between the SFD maps and the observed early-typegalaxy reddenings. If this is due to an error in the SFD maps, then itcan be corrected with a small (13%) multiplicative dipole term. Weargue, however, that this difference is more likely to be due to a small(0.01 mag) systematic error in the measured B-V colors of the early-typegalaxies. This interpretation is supported by a smaller, independentdata set (globular cluster and RR Lyrae stars), which yields a resultinconsistent with the early-type galaxy residual dipole. BH reddeningsare found to have no significant systematic residuals, apart from theknown problem in the region 230^deg
| E and S0 galaxies in the central part of the Coma cluster: ages, metal abundances and dark matter
Mean ages and metal abundances are estimated for the stellar populationsin a sample of 115 E and S0 galaxies in the central 64 arcmin × 70arcmin of the Coma cluster. The estimates are based on the absorptionline indices Mg2, and HβG, and themass-to-light ratios (M/L). Single stellar population models fromVazdekis et al. were used to transform from the measured line indicesand M/L ratios to mean ages and mean metal abundances ([Mg/H] and[Fe/H]). The non-solar abundance ratios [Mg/Fe] were taken into accountby assuming that for a given age and iron abundance, a [Mg/Fe] differentfrom solar will affect the Mg2 index but not the M/L ratio orthe and HβG indices. The derived ages andabundances are the luminosity-weighted mean values for the stellarpopulations in the galaxies.By comparing the mean ages derived from theMg2-HβG diagram with those derived from theMg2-M/L diagram, we estimate the variations of the fractionof dark matter. Alternatively, the difference between the two estimatesof the mean age may be caused by variations in the initial mass functionor any non-homology of the galaxies.The distributions of the derived mean ages and abundances show thatthere are real variations in both the mean ages and the abundances. Wefind an intrinsic rms scatter of [Mg/H], [Fe/H] and [Mg/Fe] of 0.2 dex,and an intrinsic rms scatter of the derived ages of 0.17 dex. Themagnesium abundances [Mg/H] and the abundance ratios [Mg/Fe] are bothstrongly correlated with the central velocity dispersions of thegalaxies, while the iron abundances [Fe/H] are uncorrelated with thevelocity dispersions. Further, [Mg/H] and [Fe/H] are stronglyanticorrelated with the mean ages of the galaxies. This is not the casefor [Mg/Fe].We have tested whether the slopes of the scaling relations between theglobal parameters for the galaxies (the Mg2-σ relation,the -σ relation, the HβG-σrelation and the Fundamental Plane) are consistent with the relationbetween the ages, the abundances and the velocity dispersions. We findthat all the slopes, except the slope of the Fundamental Plane, can beexplained in a consistent way as resulting from a combination betweenvariations of the mean ages and the mean abundances as functions of thevelocity dispersions. The slope of the Fundamental Plane is `steeper'than predicted from the variations in the ages and abundances.Because of the correlation between the mean ages and the meanabundances, substantial variations in the ages and the abundances arepossible while maintaining a low scatter of all the scaling relations.When this correlation is taken into account, the observed scatter of thescaling relations is consistent with the rms scatter in the derived agesand abundances at a given velocity dispersion.
| The peculiar motions of early-type galaxies in two distant regions - II. The spectroscopic data
We present the spectroscopic data for the galaxies studied in the EFARproject, which is designed to measure the properties and peculiarmotions of early-type galaxies in two distant regions. We have obtained1319 spectra of 714 early-type galaxies over 33 observing runs on 10different telescopes. We describe the observations and data reductionsused to measure redshifts, velocity dispersions and the Mgb and Mg_2Lick linestrength indices. Detailed simulations and intercomparison ofthe large number of repeat observations lead to reliable error estimatesfor all quantities. The measurements from different observing runs arecalibrated to a common zero-point or scale before being combined,yielding a total of 706 redshifts, 676 velocity dispersions, 676 Mgblinestrengths and 582 Mg_2 linestrengths. The median estimated errors inthe combined measurements are Delta cz=20 km s^-1, Delta sigma sigma=9.1 per cent, Delta Mgb Mgb=7.2 per cent and Delta Mg_2=0.015 mag.Comparison of our measurements with published data sets shows nosystematic errors in the redshifts or velocity dispersions, and onlysmall zero-point corrections to bring our linestrengths on to thestandard Lick system. We have assigned galaxies to physical clusters byexamining the line-of-sight velocity distributions based on EFAR andZCAT redshifts, together with the projected distributions on the sky. Wederive mean redshifts and velocity dispersions for these clusters, whichwill be used in estimating distances and peculiar velocities and to testfor trends in the galaxy population with cluster mass. The spectroscopicparameters presented here for 706 galaxies combine high-quality data,uniform reduction and measurement procedures, and detailed erroranalysis. They form the largest single set of velocity dispersions andlinestrengths for early-type galaxies published to date.
| Fundamental plane distances to early-type field galaxies in the South Equatorial Strip. I. The spectroscopic data
Radial velocities and central velocity dispersions are derived for 238E/S0 galaxies from medium-resolution spectroscopy. New spectroscopicdata have been obtained as part of a study of the Fundamental Planedistances and peculiar motions of early-type galaxies in three selecteddirections of the South Equatorial Strip, undertaken in order toinvestigate the reality of large-scale streaming motion; results of thisstudy have been reported in Müller et al. (1998). The new APM SouthEquatorial Strip Catalog (-17fdg 5 < delta < +2fdg 5) was used toselect the sample of field galaxies in three directions: (1) 15h10 -16h10; (2) 20h30 - 21h50; (3) 00h10 - 01h30. The spectra obtained have amedian S/N per Å of 23, an instrumental resolution (FWHM) of ~ 4Å, and the spectrograph resolution (dispersion) is ~ 100 kms-1. The Fourier cross-correlation method was used to derivethe radial velocities and velocity dispersions. The velocity dispersionshave been corrected for the size of the aperture and for the galaxyeffective radius. Comparisons of the derived radial velocities with datafrom the literature show that our values are accurate to 40 kms-1. A comparison with results from Jo rgensen et al. (1995)shows that the derived central velocity dispersion have an rms scatterof 0.036 in log sigma . There is no offset relative to the velocitydispersions of Davies et al. (1987).
| The tilt of the Fundamental Plane of early-type galaxies: wavelength dependence
The photometric parameters R_e and mu_e of 74 early-type (E+S0+S0a)galaxies within 2 deg projected radius from the Coma cluster centre arederived for the first time in the near-infrared H band (1.65 μm).These are used, coupled with measurements of the central velocitydispersion sigma found in the literature, to determine the H-bandFundamental Plane (FP) relation of this cluster: logR_e~Alogsigma+bmu_e. The same procedure is applied to previouslyavailable photometric data in the BVrIK bands, to perform amultiwavelength study of the FP relation. Because systematicuncertainties in the value of the FP parameters are introduced both bythe choice of the fitting algorithm used to derive the FP template, andby the presence of statistical biases connected with the sampleselection procedure, we emphasize the importance of deriving the FPparameters in the six different photometric bands using an identicalfitting algorithm, and appropriate corrections to eliminate the effectsof sample incompleteness. Once these corrections are applied, we findthat the FP b coefficient is stable with wavelength (~0.35+/-0.02),while the A coefficient increases significantly with increasingwavelength: from ~1.35 to ~1.70 (+/-0.1) from the optical to theinfrared, in agreement with an earlier result presented recently byPahre and Djorgovski. Therefore the slope of the FP relation, althoughchanging with wavelength, never approaches the virial theoremexpectation A=2.0 when the central velocity dispersion only is used tobuild the FP. We also find that the magnitude of the slope change can beentirely explained by the presence of the well-known relation betweencolour and magnitude among early-type galaxies. We conclude that thetilt of the Fundamental Plane is significant, and must be the result ofsome form of broken homology among early-type galaxies, while itswavelength dependence derives from whatever mechanism (currently thepreferred one is the existence of a mass-metal content sequence)produces the colour-magnitude relation in those galaxies.
| The Universality of the Fundamental Plane of E and S0 Galaxies: Spectroscopic Data
We present central velocity dispersion measurements for 325 early-typegalaxies in eight clusters and groups of galaxies, including newobservations for 212 galaxies. The clusters and groups are the A262,A1367, Coma (A1656), A2634, Cancer, and Pegasus Clusters and the NGC 383and NGC 507 Groups. The new measurements were derived frommedium-dispersion spectra that cover 600 Å centered on the Mg I btriplet at lambda ~ 5175 Å. Velocity dispersions were measuredusing the Tonry & Davis cross-correlation method, with a typicalaccuracy of 6%. A detailed comparison with other data sources is made.
| The Universality of the Fundamental Plane of E and S0 Galaxies: Sample Definition and I-Band Photometric Data
As part of a project to compare the fundamental plane and Tully-Fisherdistance scales, we present here I-band CCD photometry for 636early-type galaxies in eight clusters and groups of galaxies. These arethe A262, A1367, Coma (A1656), A2634, Cancer and Pegasus Clusters, andthe NGC 383 and NGC 507 Groups. Sample selection, cluster properties,and cluster membership assignment criteria are discussed. We presentphotometric parameters that are used in the fundamental plane relation,the effective radius r_e, and the effective surface brightness mu_e, asderived from a r^1/4 fit to the observed radial photometric profile ofeach galaxy. A comparison with similar data found in the literature forthe Coma Cluster shows that large systematic uncertainties can beintroduced in the measurement of r_e and mu_e by the particular methodused to derive those parameters. However, the particular combination ofthese two parameters that enters in the fundamental plane relation is aquantity that can be measured with high accuracy.
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