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Публикации по объекту
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.
| The build-up of the Coma cluster by infalling substructures
We present a new multiwavelength analysis of the Coma clustersubclustering based on recent X-ray data and on a compilation of nearly900 redshifts. We characterize subclustering using the Serna &Gerbal (1996, A&A, 309, 65) hierarchical method, which makes use ofgalaxy positions, redshifts, and magnitudes, and identify 17 groups. Oneof these groups corresponds to the main cluster, one is the well knowngroup associated with the infalling galaxy NGC 4839, and one isassociated with NGC 4911/NGC 4926. About one third of the 17 groups havevelocity distributions centered on the velocities of the very brightcluster galaxies they contain (magnitudes R < 13). In order to searchfor additional substructures, we made use of the isophotes of X-raybrightness residuals left after the subtraction of the best-fitβ-model from the overall X-ray gas distribution (Neumann et al.2003, A&A, 400, 811). We selected galaxies within each of theseisophotes and compared their velocity distributions with that of thewhole cluster. We confirm in this way the two groups associated,respectively, with NGC 4839, and with the southern part of the extendedwestern substructure visible in X-rays. We discuss the group propertiesin the context of a scenario in which Coma is built by the accretion ofgroups infalling from the surrounding large-scale structure. We estimatethe recent mass accretion rate of Coma and compare it with hierarchicalmodels of cluster evolution.
| Star formation history in early-type galaxies - I. The line absorption indices diagnostics
To unravel the formation mechanism and the evolutionary history ofelliptical galaxies (EGs) is one of the goals of modern astrophysics. Ina simplified picture of the issue, the question to be answered iswhether they have formed by hierarchical merging of pre-existingsubstructures (maybe disc galaxies) made of stars and gas, with eachmerging event probably accompanied by strong star formation, orconversely, whether they originated from the early aggregation of lumpsof gas turned into stars in the remote past via a burst-like episodeever since followed by quiescence so as to mimic a sort of monolithicprocess. Even if the two alternatives seem to oppose each other,actually they may both contribute to shaping the final properties of EGsas seen today. Are there distinct signatures of the underlying dominantprocess in the observational data? To this aim we have examined the lineabsorption indices on the Lick system of the normal, field EGs of Tragerand the interacting EGs (pair- and shell-objects) of Longhetti et al.The data show that both normal, field and interacting galaxies have thesame scattered but smooth distribution in the Hβ versus [MgFe]plane even if the interacting ones show a more pronounced tail towardhigh Hβ values. This may suggest that a common physical cause is atthe origin of their distribution. There are two straightforwardinterpretations of increasing complexity. (i) EGs span true large rangesof ages and metallicities. A young age is the signature of theaggregation mechanism, each event accompanied by metal enrichment. Thissimple scheme cannot, however, explain other spectro-photometricproperties of EGs and has to be discarded. (ii) The bulk population ofstars is old but subsequent episodes of star formation scatter the EGsin the diagnostic planes. However, this scheme would predict anoutstanding clump at low Hβ values, contrary to what is observed.The model can be cured by supposing that the primary star formationactivity lasted for a significant fraction of the Hubble time (5<=T<= 13 Gyr) accompanied by global metal enrichment. The`younger' galaxies are more metal-rich. The later burst of starformation should be small otherwise too many high-Hβ objects wouldbe observed. Therefore, the distribution of normal, pair- andshell-galaxies in the Hβ versus [MgFe] plane is due to global metalenrichment. Even though the above schemes provide a formal explanation,they seem to be too demanding because of the many ad hoc ingredientsthat have to be introduced. Furthermore, they neglect theobservationally grounded hint that the stellar content of EGs is likelyto be enhanced in α-elements with [α/Fe] ranging from 0.1 to0.4 dex. Here we propose a new scheme, in which the bulk dispersion ofgalaxies in the Hβ versus [MgFe] plane is caused by a differentmean degree of enhancement. In this model, neither the large age rangesnor the universal enrichment law for the old component are required andthe observed distribution along Hβ is naturally recovered.Furthermore, later bursts of stellar activity are a rare event,involving only those galaxies with very high Hβ (roughly >2.5).Finally, simulations of the scatter in broad-band colours of EGs seem toconfirm that the bulk stars have formed in the remote past, and thatmergers and companion star formation in a recent past are not likely,unless the intensity of the secondary activity is very small.
| 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.
| Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500
| 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
| 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 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.
| Spatially resolved spectroscopy of Coma cluster early-type galaxies. II. The minor axis dataset
We present minor axis, offset major axis and one diagonal long slitspectra for 10 E and S0 galaxies of the Coma cluster drawn from amagnitude-limited sample studied before. We derive rotation curves,velocity dispersion profiles and the H3 and H4coefficients of the Hermite decomposition of the line of sight velocitydistribution. Moreover, we derive the line index profiles of Mg, Fe andHβ line indices and assess their errors. The data will be used toconstruct dynamical models of the galaxies and study their stellarpopulations. Tables 3 and 4 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/395/753
| 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.
| Spectroscopic constraints on the stellar population of elliptical galaxies in the Coma cluster
Near-infrared spectra for a sample of 31 elliptical galaxies in the Comacluster are obtained. The galaxies are selected to be ellipticals (nolenticulars), with a large spatial distribution, covering both the coreand outskirts of the cluster (i.e. corresponding to regions with largedensity contrasts). COsp (2.3-μm) absorption indices,measuring the contribution from intermediate-age red giant andsupergiant stars to the near-infrared light of the ellipticals, are thenestimated. It is found that the strength of COsp features inelliptical galaxies increases from the core (r<0.2°) to theoutskirts (r>0.2°) of the Coma cluster. Using the Mg2strengths, it is shown that the observed effect is not caused bymetallicity and is mostly caused by the presence of a younger population(giant and supergiant stars) in ellipticals in the outskirts(low-density region) of the cluster. Using the COsp features,the origin of the scatter on the near-infrared Fundamental Plane (therelation between the effective diameter, effective surface brightnessand velocity dispersion) of elliptical galaxies is studied. Correctingthis relation for contributions from the red giant and supergiant stars,the rms scatter reduces from 0.077 to 0.073dex. Although measurable, thecontribution from these intermediate-age stars to the scatter on thenear-infrared Fundamental Plane of ellipticals is only marginal. Arelation is found between the COsp and V-K colours ofellipticals, corresponding to a slope of 0.036+/-0.016, significantlyshallower than that from the Mg2-(V-K) relation. This isstudied using stellar synthesis models.
| Spectrophotometry of Nearby Field Galaxies: The Data
We have obtained integrated and nuclear spectra as well as U, B, Rsurface photometry for a representative sample of 196 nearby galaxies.These galaxies span the entire Hubble sequence in morphological type, aswell as a wide range of luminosities (MB=-14 to -22). Here wepresent the spectrophotometry for these galaxies. The selection of thesample and the U, B, R surface photometry is described in a companionpaper. Our goals for the project include measuring the current starformation rates and metallicities of these galaxies, and elucidatingtheir star formation histories, as a function of luminosity andmorphology. We thereby extend the work of Kennicutt to lower luminositysystems. We anticipate that our study will be useful as a benchmark forstudies of galaxies at high redshift. We describe the observing, datareduction, and calibration techniques and demonstrate that ourspectrophotometry agrees well with that of Kennicutt. The spectra spanthe range 3550-7250 Å at a resolution (FWHM) of ~6 Å andhave an overall relative spectrophotometric accuracy of ~+/-6%. Wepresent a spectrophotometric atlas of integrated and nuclear rest-framespectra as well as tables of equivalent widths and synthetic colors. Theatlas and tables of measurements will be made available electronically.We study the correlations of galaxy properties determined from thespectra and images. Our findings include: (1) galaxies of a givenmorphological class display a wide range of continuum shapes andemission-line strengths if a broad range of luminosities are considered,(2) emission-line strengths tend to increase and continua tend to getbluer as the luminosity decreases, and (3) the scatter on the generalcorrelation between nuclear and integrated Hα emission-linestrengths is large.
| Surface Photometry of Nearby Field Galaxies: The Data
We have obtained integrated spectra and multifilter photometry for arepresentative sample of ~200 nearby galaxies. These galaxies span theentire Hubble sequence in morphological type, as well as a wide range ofluminosities (MB=-14 to -22) and colors (B-R=0.4-1.8). Herewe describe the sample selection criteria and the U, B, R surfacephotometry for these galaxies. The spectrophotometric results will bepresented in a companion paper. Our goals for the project includemeasuring the current star formation rates and metallicity of thesegalaxies, and elucidating their star formation histories, as a functionof luminosity and morphology. We thereby extend the work of Kennicutt tolower luminosity systems. We anticipate that our study will be useful asa benchmark for studies of galaxies at high redshift. We discuss theobserving, data reduction, and calibration techniques and show that ourphotometry agrees well with previous work in those cases in whichearlier data are available. We present an atlas of images, radialsurface brightness profiles, and color profiles as well as tables ofderived parameters. The atlas and tables of measurements will be madeavailable electronically. We study the correlations of galaxy propertiesdetermined from the galaxy images. Our findings include the following:(1) colors determined within the effective radius correlate better withmorphological type than with MB and (2) 50% of thelow-luminosity galaxies are bluest in their centers.
| 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.
| 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.
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