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|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.
|Kinematic properties and stellar populations of faint early-type galaxies - I. Velocity dispersion measurements of central Coma galaxies|
We present velocity dispersion measurements for 69 faint early-typegalaxies in the core of the Coma cluster, spanning -22.0<~MR<~-17.5 mag. We examine the L-σ relation forour sample and compare it to that of bright elliptical galaxies (Es)from the literature. The distribution of the the faint early-typegalaxies in the L-σ plane follows the relationL~σ2.01+/-0.36, which is significantly shallower fromL~σ4 as defined for the bright Es. While increasedrotational support for fainter early-type galaxies could account forsome of the difference in slope, we show that it cannot explain it. Wealso investigate the colour-σ relation for our Coma galaxies.Using the scatter in this relation, we constrain the range of galaxyages as a function of their formation epoch for different formationscenarios. Assuming a strong coordination in the formation epoch offaint early-type systems in Coma, we find that most had to be formed atleast 6 Gyr ago and over a short 1-Gyr period.
|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.
|The Extinction and Distance of Maffei 1|
We have obtained low- and high-resolution spectra of the core of thehighly reddened elliptical galaxy Maffei 1. From these data, we haveobtained the first measurement of the Mg2 index and havemeasured the velocity dispersion and radial velocity with improvedaccuracy. To evaluate the extinction, a correlation between theMg2 index and effective V-I color has been established forelliptical galaxies. Using a new method for correcting for effectivewavelength shifts, the V-I color excess reveals that the optical depthof Galactic dust at 1 μm is 1.69+/-0.07. Thus,AV=4.67+/-0.19 mag, which is lower by 0.4 mag than previouslythought. To establish the distance, the fundamental plane for ellipticalgalaxies has been constructed in I. The velocity dispersion of Maffei 1,measured to be 186.8+/-7.4 km s-1, in combination with modernwide-field photometry in I, leads to a distance of 2.92+/-0.37 Mpc. TheDn-σ relation, which is independently calibrated, gives3.08+/-0.85 and 3.23+/-0.67 Mpc from photometry in B and K',respectively. The weighted mean of the three estimates is 3.01+/-0.30Mpc, which is lower than distances judged with reference to M32 and thebulge of M31 from the brightest stars seen at K'. Since the luminosityof asymptotic giant branch stars at K' is strongly dependent on age, thelower distance suggests that the last epoch of star formation in Maffei1 occurred farther in the past than in these other systems. The distanceand luminosity make Maffei 1 the nearest giant elliptical galaxy. In theabsence of extinction, the galaxy would be among the brightest in thesky and would have an apparent size 2/3 that of the full Moon. Theradial velocity of Maffei 1 is +66.4+/-5.0 km s-1,significantly higher than the accepted value of -10 km s-1.The Hubble distance corresponding to the mean velocity of Maffei 1,Maffei 2, and IC 342 is 3.5 Mpc. Thus, it is unlikely that Maffei 1 hashad any influence on Local Group dynamics.
|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.
|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
|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.
|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.
|The First Hour of Extragalactic Data of the Sloan Digital Sky Survey Spectroscopic Commissioning: The Coma Cluster|
On 1999 May 26, one of the Sloan Digital Sky Survey (SDSS) fiber-fedspectrographs saw astronomical first light. This was followed by thefirst spectroscopic commissioning run during the dark period of 1999June. We present here the first hour of extragalactic spectroscopy takenduring these early commissioning stages: an observation of the Comacluster of galaxies. Our data samples the southern part of this cluster,out to a radius of 1.5d (1.8 h-1 Mpc, approximately to thevirial radius) and thus fully covers the NGC 4839 group. We outline inthis paper the main characteristics of the SDSS spectroscopic systemsand provide redshifts and spectral classifications for 196 Comagalaxies, of which 45 redshifts are new. For the 151 galaxies in commonwith the literature, we find excellent agreement between our redshiftdeterminations and the published values, e.g., for the largesthomogeneous sample of galaxies in common (63 galaxies observed byColless & Dunn) we find a mean offset of 3 km s -1 and anrms scatter of only 24 km s -1. As part of our analysis, wehave investigated four different spectral classification algorithms:measurements of the spectral line strengths, a principal componentdecomposition, a wavelet analysis and the fitting of spectral synthesismodels to the data. We find that these classification schemes are inbroad agreement and can provide physical insight into the evolutionaryhistories of our cluster galaxies. We find that a significant fraction(25%) of our observed Coma galaxies show signs of recent star formationactivity and that the velocity dispersion of these active galaxies(emission-line and poststarburst galaxies) is 30% larger than theabsorption-line galaxies. We also find no active galaxies within thecentral (projected) 200 h-1 kpc of the cluster. The spatialdistribution of our Coma active galaxies is consistent with that foundat higher redshift for the CNOC1 cluster survey. Beyond the core region,the fraction of bright active galaxies appears to rise slowly out to thevirial radius and are randomly distributed within the cluster with noapparent correlation with the potential merger or postmerger of the NGC4839 group. We briefly discuss possible origins of this recent galaxystar formation.
|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 (184.108.40.206) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|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 (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|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).
|Galaxy disruption as the origin of intracluster light in the Coma cluster of galaxies.|
Although the existence of a faint background of starlight in the core ofthe Coma cluster has been well established (1,2), its origin isuncertain. This vast sea of stars could have formed outside thegalaxies, using gas left over from the time of the cluster's birth.Alternatively, it might be the accumulated debris generated byinteractions between the galaxies over the lifetime of the cluster (3).Here we report the discovery of three large, low surface brightnessfeatures in the Coma cluster; the most spectacular is a plume-likestructure, 130 kpc long, in the cluster's heart. These structures willdisperse over the next one to two billion years, thereby enhancing thegeneral background light. If this epoch is typical, we argue that asignificant fraction -- perhaps even most -- of the intracluster lightresults from a steady accumulation of tidal debris generated duringgalaxy-galaxy and galaxy-cluster interactions.
|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.
|A catalogue of Mg_2 indices of galaxies and globular clusters|
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 18.104.22.168. Table 2 is available both in text and electronic form.
|Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies|
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
|Dwarf Galaxies in the Coma Cluster. II. Photometry and Analysis|
We use the data set derived in our previous paper (Secker & Harris1997) to study the dwarf galaxy population in the central =~ 700arcmin(2) of the Coma cluster, the majority of which are early-typedwarf elliptical (dE) galaxies. Analysis of thestatistically-decontaminated dE galaxy sequence in the color-magnitudediagram reveals that the mean dE color at R = 18.0 mag is (B-R) =~ 1.4mag, but that a highly significant trend of color with magnitude exists(Delta (B-R)/Delta R = -0.056+/-0.002 mag) in the sense that fainter dEsare bluer and thus presumably more metal-poor. The mean color of thefaintest dEs in our sample is (B-R) =~ 1.15 mag, consistent with a colormeasurement of the diffuse intracluster light in the Coma core. Thisintracluster light could then have originated from the tidal disruptionof faint dEs in the cluster core. The total galaxy luminosity function(LF) is well modeled as the sum of a log-normal distribution for thegiant galaxies, and a Schechter function for the dE galaxies with afaint-end slope alpha = -1.41+/-0.05. This value of alpha is consistentwith those measured for the Virgo and Fornax clusters. The spatialdistribution of the faint dE galaxies (19.0 < R <= 22.5 mag) iswell fit by a standard King model with a central surface density ofSigma_0 = 1.17 dEs arcmin(-2) and a core radius R_c = 22.15 arcmin ( =~0.46h(-1) Mpc). This core is significantly larger than the R_c = 13.71arcmin ( =~ 0.29h(-1) Mpc) found for the cluster giants and the brighterdEs (R <= 19.0 mag), again consistent with the idea that faint dEs inthe dense core have been disrupted. Finally, we find that most dEsbelong to the general Coma cluster potential rather than as satellitesof individual giant galaxies: An analysis of the number counts around 10cluster giants reveals that they each have on average 4+/- 1 dEcompanions within a projected radius of 13.9h(-1) kpc. (SECTION:Galaxies)
|The peculiar motions of early-type galaxies in two distant regions. III - The photometric data|
We present R-band CCD photometry for 776 galaxies observed in the EFARproject. The photometry is compared with photoelectric data, showingthat a common zero-point good to better than 1 per cent and a precisionof 0.03 mag per zero-point have been achieved. We give the circularlyaveraged surface brightness profiles and the photometric parameters ofthe 762 program galaxies, D(n) diameters, half-luminosity radii, totalmagnitudes, and average effective surface brightnesses. More than 80percent of the profiles have a global S/N ratio larger than 300. Theextrapolation needed to derive total magnitudes is less than 10 percentfor 80 percent of the fits. More than 80 percent of the galaxies havemean effective surface brightness larger than the observed skybrightness. In 90 percent of the profiles the estimate of thecontamination of the sky by the galaxy light is less than 1 percent. Wederive total magnitudes and half-luminosity radii to better than 0.15mag and 25 percent, respectively, for 90 percent of our sample. Incontrast, external comparisons show that data in the literature can bestrongly affected by systematic errors due to large extrapolations,small radial range, sky subtraction errors, seeing effects, and the useof a simple R exp 1/4 fit. The resulting errors can easily amount tomore than 0.5 mag in the total magnitudes and 50 percent in thehalf-luminosity radii.
|Abell 2199 and Abell 2634 revisited|
Previous D_n-sigma work found surprisingly large negative peculiarvelocities for Abell 2199 and Abell 2634. In order to assess theseresults independently we have made new spectroscopic and photometricobservations. We report 141 new redshift, velocity dispersion (sigma)and Mg_2 index measurements, and photometry for 79 early-type galaxies.Special attention has been paid to linking the new sigma measurements onto a standard system that minimizes systematic errors. While the Abell2199 sigma measurements are in good agreement with our previouslyreported FLEX values, for Abell 2634 galaxies the new sigmas aresystematically lower. The FLEX measurements for some Abell 2634 galaxiesappear to have been erroneous due to a smearing problem with the CCDdetector. The new photometric data are in excellent agreement withpreviously reported values. We also present a new compilation of datafor 72 early-type Coma cluster galaxies. Assuming that the Coma clusterlies at rest with respect to the cosmic microwave background frame, wederive peculiar velocities of -160+/-380 and -670+/-490 km s^-1 forAbell 2199 and Abell 2634 respectively. We estimate that the likelysystematic errors on these measurements are less than 200kms^-1. Thederived peculiar velocities are considerably less than previousestimates and are not significantly different from zero.
|The Relative Distance Between the Clusters of Galaxies A2634 and Coma|
The Tully-Fisher (TF) and Fundamental Plane (FP) relations are used toobtain two independent estimates of the relative distance between theclusters A2634 and Coma. Previously published studies of A2634 showed alarge discrepancy between the distance estimates obtained with the TFand the \dns\ relations, questioning the reliability ofredshift-independent distances obtained using these relations. Becauseof the importance of this issue, we have obtained new distance estimatesfor A2634, based on much larger samples than previously used, andselected according to rigorous membership criteria. New I band CCDphotometry for 175 galaxies, new 21 cm observations of 11 galaxies, andnew velocity dispersion measurements for 62 galaxies are used togetherwith previously published data in building these samples. As part of alarger project to compare the TF and FP distance-scales, we haveobtained a new FP template using for the first time I band photometry.The template is derived using a sample of 109 E and S0 galaxies that aremembers of the Coma cluster. Its parameters are in very good agreementwith recent determinations of the FP obtained at shorter wavelengths.The uncertainty with which the FP can provide peculiar velocityestimates for single galaxies is =~ 0.43 mag in the distance modulus, or20% of the distance. This uncertainty is slightly larger than thetypical uncertainty that characterizes TF estimates. However thisdisadvantage is partly compensated by the fact that the sampleincompleteness bias has a less severe effect on FP cluster distanceestimates than it has on the corresponding TF distance estimates. Also,cluster membership is more readily established for early-type objectsthan for spirals. After the appropriate corrections for sampleincompleteness have been taken into account, we find the TF and FPdistance estimates to be in good agreement, both indicating that A2634has a negligibly small peculiar velocity with respect to the CosmicMicrowave Background reference frame. Because of the high accuracy withwhich the two distance estimates have been obtained, their agreementstrongly supports the universality of the TF and FP relations, andtherefore their reliability for the estimate of redshift-independentdistances.
|The Peculiar Motions of Early-Type Galaxies in Two Distant Regions. I. Cluster and Galaxy Selection|
The EFAR project is a study of 736 candidate elliptical galaxies in 84clusters lying in two regions, toward Hercules-Corona Borealis andPerseus-Pisces-Cetus, at distances cz ~ 6000-15,000 km s^-1^. In thispaper (the first of a series), we present an introduction to the EFARproject and describe in detail the selection of the clusters andgalaxies in our sample. Fundamental data for the galaxies and clustersare given, including accurate new positions for each galaxy andredshifts for each cluster. The galaxy selection functions aredetermined by using diameters measured from Schmidt sky survey imagesfor 2185 galaxies in the cluster fields. Future papers in this serieswill present the spectroscopic and photometric observations of thissample, investigate the properties of the fundamental plane forelliptical galaxies, and determine the large- scale peculiar velocityfields in these two regions of the universe.
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