Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
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.
| Hot stars in old stellar populations: a continuing need for intermediate ages
We investigate the effect of a low-level contamination of hot, old,metal-poor starlight on the inferred stellar populations of early-typegalaxies in the core of the Coma Cluster. We find that the requiredcorrection to the Balmer and metal absorption-line strengths for old,metal-poor stars does not significantly affect the inferred age of thestellar population when the Hβ strength is large. Intermediate-agedpopulations are therefore still needed to explain enhanced Balmer-linestrengths in early-type galaxies. This gives us increased confidence inour age estimates for these objects. For galaxies with weak Balmer-linestrengths corresponding to very old populations (t > 10 Gyr),however, a correction for hot stars may indeed alter the inferred age,as previously suggested. Finally, the inferred metallicity [Z/H] willalways be higher after any correction for old, metal-poor starlight thanif it were not taken into account, but the enhancement ratios [E/Fe]will strengthen only slightly.
| 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.
| Line-of-Sight Reddening Predictions: Zero Points, Accuracies, the Interstellar Medium, and the Stellar Populations of Elliptical Galaxies
Revised (B-V)0-Mg2 data, which are used to testreddening predictions, are presented for 402 elliptical galaxies. Thesereddening predictions can tell us both what the intrinsic errors are inthis relationship among gE galaxy stellar populations as well as detailsof nearby structure in the interstellar medium (ISM) of our Galaxy, andof the intrinsic errors in reddening predictions. Using least-squaresfits, the explicit 1 σ errors in reddenings predicted by theBurstein-Heiles (BH) method and the Schlegel and coworkers (IR) methodare calculated, as well as the 1 σ observational error in the(B-V)0-Mg2 for gE galaxies. It is found that indirections with E(B-V)<0.100 mag (where most of these galaxies lie),1 σ errors in the IR reddening predictions are 0.006-0.009 mag inE(B-V), those for BH reddening predictions are 0.011 mag, and the 1σ agreement between the two reddening predictions is 0.007 mag.The IR predictions have an accuracy of 0.010-0.011 mag in directionswith E(B-V)>=0.100 mag, significantly better than those of the BHpredictions (0.024-0.025). Both methods yield good evidence thatgas-to-dust variations that vary by a factor of 3, both high and low,exist along many lines of sight in our Galaxy. Both methods also predictmany directions with E(B-V)<0.015 mag, despite the difference in zeropoint that each has assumed. The ~0.02 higher reddening zero point inE(B-V) previously determined by Schlegel and coworkers is confirmed,primarily at the Galactic poles. Independent evidence of reddening atthe north Galactic pole (NGP) is reviewed, with the conclusion thatdirections still exist at the NGP that have E(B-V)<<0.01. Twolines of evidence suggest that IR reddenings are overpredicted indirections with high gas-to-dust ratios. As high gas-to-dust directionsin the ISM also include the Galactic poles, this overprediction is thelikely cause of the E(B-V)~0.02 mag larger IR reddening zero pointrelative to that of BH.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| Spatially resolved spectroscopy of Coma cluster early-type galaxies. III. The stellar population gradients
Based on Paper I of this series (Mehlert et al. \cite{Mehlert00}), wederive central values and logarithmic gradients for the Hβ, Mg andFe indices of 35 early-type galaxies in the Coma cluster. We find thatpure elliptical galaxies have on average slightly higher velocitydispersions, lower Hβ, and higher metallic line-strengths thangalaxies with disks (S0). The latter form two families, one comparableto the ellipticals and a second one with significantly higher Hβ,and weaker metallic lines. Our measured logarithmic gradients within theeffective radius are ~ -0.037, ~ -0.029, ~ +0.017 and ~ -0.063. The gradients strongly correlate with the gradientsof sigma , but only weakly with the central index values and galaxyvelocity dispersion. Using stellar population models with variableelement abundance ratios from Thomas et al. (\cite{Thomas03a}) we deriveaverage ages, metallicities and [α/Fe] ratios in the center and atthe effective radius. We find that the α/Fe ratio correlates withvelocity dispersion and drives 30% of the Mg-sigma relation, theremaining 70% being caused by metallicity variations. We confirmprevious findings that part of the lenticular galaxies in the Comacluster host very young ( ~ 2 Gyr) stellar populations, hence must haveexperienced relatively recent star formation episodes. Again inaccordance with previous work we derive negative metallicity gradients (~ -0.16 dex per decade) that are significantly flatter than what isexpected from gaseous monolithic collapse models, pointing to theimportance of mergers in the galaxy formation history. Moreover, themetallicity gradients correlate with the velocity dispersion gradients,confirming empirically earlier suggestions that the metallicity gradientin ellipticals is produced by the local potential well. The gradients inage are negligible, implying that no significant residual star formationhas occurred either in the center or in the outer parts of the galaxies,and that the stellar populations at different radii must have formed ata common epoch. For the first time we derive the gradients of theα/Fe ratio and find them very small on average. Hence, α/Feenhancement is not restricted to galaxy centers but it is a globalphenomenon. Our results imply that the Mg-sigma local relation inside agalaxy, unlike the global Mg-sigma relation, must be primarily drivenby metallicity variations alone. Finally we note that none of thestellar population parameters or their gradients depend on the densityprofile of the Coma cluster, even though it spans 3 dex in density.Appendix A (Tables A.1-A.3) is only available in electronic form athttp://www.edpsciences.org
| Stellar populations in early-type Coma cluster galaxies - I. The data
We present a homogeneous and high signal-to-noise ratio data set (meanS/N ratio of ~60 Å-1) of Lick/IDS stellar populationline indices and central velocity dispersions for a sample of 132 bright(bj<= 18.0) galaxies within the central 1°(≡1.26h-1 Mpc) of the nearby rich Coma cluster (A1656). Ourobservations include 73 per cent (100 out of 137) of the totalearly-type galaxy population (bj<= 18.0). Observationswere made with the William Herschel 4.2-m telescope and theAUTOFIB2/WYFFOS multi-object spectroscopy instrument (resolution of~2.2-Å FWHM) using 2.7-arcsec diameter fibres (≡0.94h-1 kpc). The data in this paper have well-characterizederrors, calculated in a rigorous and statistical way. Data are comparedwith previous studies and are demonstrated to be of high quality andwell calibrated on to the Lick/IDS system. Our data have median errorsof ~0.1 Å for atomic line indices, ~0.008 mag for molecular lineindices and 0.015 dex for velocity dispersions. This work provides awell-defined, high-quality baseline at z~ 0 for studies of medium- tohigh-redshift clusters. Subsequent papers will use this data set toprobe the stellar populations (which act as fossil records of galaxyformation and evolution) and the spectrophotometric relations of thebright early-type galaxies within the core of the Coma cluster.
| 1.65-μm (H -band) surface photometry of galaxies - VIII. The near-IR κ space at z =0
We present the distribution of a statistical sample of nearby galaxiesin the κ -space (κ 1 ~logM , κ 2~logI e 3 M /L , κ 3 ~logM /L ).Our study is based on near-IR (H -band: λ =1.65μm)observations, for the first time comprising early- and late-typesystems. Our data confirm that the mean effective dynamicalmass-to-light ratio M /L of the E+S0+S0a galaxies increases withincreasing effective dynamical mass M , as expected from the existenceof the Fundamental Plane relation. Conversely, spiral and Im/BCDgalaxies show a broad distribution in M /L with no detected trend of M/L with M , the former galaxies having M /L values about twice largerthan the latter, on average. For all the late-type galaxies, the M /Lincreases with decreasing effective surface intensity I e ,consistent with the existence of the Tully-Fisher relation. Theseresults are discussed on the basis of the assumptions behind theconstruction of the κ -space and their limitations. Our study iscomplementary to a previous investigation in the optical (B -band:λ =0.44μm) and allows us to study wavelength dependences ofthe galaxy distribution in the κ -space. As a first result, wefind that the galaxy distribution in the κ 1 -κ2 plane reproduces the transition from bulgeless tobulge-dominated systems in galaxies of increasing dynamical mass.Conversely, it appears that the M /L of late-types is higher (lower)than that of early-types with the same M in the near-IR (optical). Theorigins of this behaviour are discussed in terms of dust attenuation andstar formation history.
| New clues to the evolution of dwarf early-type galaxies
Surface photometry of 18 Virgo cluster dwarf elliptical (dE) and dwarflenticular (dS0) galaxies, made by Gavazzi et al. in the H band(1.65μm) and in the B band (0.44μm), shows that the ratio of theeffective radii of these stellar systems in the B and H bands, r eB /r eH , ranges between 0.7 and 2.2. In particular,dwarf ellipticals and lenticulars with a red total colour index B -H(i.e. with 3.2
| A catalogue and analysis of local galaxy ages and metallicities
We have assembled a catalogue of relative ages, metallicities andabundance ratios for about 150 local galaxies in field, group andcluster environments. The galaxies span morphological types from cD andellipticals, to late-type spirals. Ages and metallicities were estimatedfrom high-quality published spectral line indices using Worthey &Ottaviani (1997) single stellar population evolutionary models. Theidentification of galaxy age as a fourth parameter in the fundamentalplane (Forbes, Ponman & Brown 1998) is confirmed by our largersample of ages. We investigate trends between age and metallicity, andwith other physical parameters of the galaxies, such as ellipticity,luminosity and kinematic anisotropy. We demonstrate the existence of agalaxy age-metallicity relation similar to that seen for local galacticdisc stars, whereby young galaxies have high metallicity, while oldgalaxies span a large range in metallicities. We also investigate theinfluence of environment and morphology on the galaxy age andmetallicity, especially the predictions made by semi-analytichierarchical clustering models (HCM). We confirm that non-clusterellipticals are indeed younger on average than cluster ellipticals aspredicted by the HCM models. However we also find a trend for the moreluminous galaxies to have a higher [Mg/Fe] ratio than the lowerluminosity galaxies, which is opposite to the expectation from HCMmodels.
| The Color-Magnitude Relation in Coma: Clues to the Age and Metallicity of Cluster Populations
We have observed three fields of the Coma Cluster of galaxies with anarrowband (modified Strömgren) filter system. Observed galaxiesinclude 31 in the vicinity of NGC 4889, 48 near NGC 4874, and 60 nearNGC 4839, complete to M5500=-18 in all three subclusters.Spectrophotometric classification finds all three subclusters of Coma tobe dominated by red, E-type (elliptical/S0) galaxies with a mean bluefraction, fB, of 0.10. The blue fraction increases to fainterluminosities, possible remnants of dwarf starburst population or theeffects of dynamical friction removing bright, blue galaxies from thecluster population by mergers. We find the color-magnitude (CM) relationto be well defined and linear over the range of M5500=-13 to-22. The observational error is lower than the true scatter around theCM relation, indicating that galaxies achieve their final positions inthe mass-metallicity plane by stochastic processes. After calibration tomultimetallicity models, bright elliptical galaxies are found to haveluminosity-weighted mean [Fe/H] values between -0.5 and +0.5, whereaslow-luminosity elliptical galaxies have [Fe/H] values ranging from -2 tosolar. The lack of CM relation in our continuum color suggests that asystematic age effect cancels the metallicity effects in this bandpass.This is confirmed with our age index Δ(bz-yz), which finds a weakcorrelation between luminosity and mean stellar age in ellipticalgalaxies such that the stellar populations of bright elliptical galaxiesare 2-3 Gyrs younger than low-luminosity elliptical galaxies. Withrespect to environmental effects, there is a slight decreasingmetallicity gradient with respect to distance to each subcluster center,strongest around NGC 4874. Since NGC 4874 is the dynamic and X-raycenter of the Coma Cluster, this implies that environmental effects onlow-luminosity elliptical galaxies are strongest at the cluster corecompared with outlying subgroups.
| 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.
| Galaxy associations within the Coma cluster.
The mean redshift of the core of the Coma cluster -- cz=6953 kms-1 and its dispersion σ=949 km s-1 areobtained by means of the analysis of the substructures of this clusterby using the S-tree method. The existence of three subgroups of galaxiesis revealed, one of them is associated with the cD galaxy NGC 4874, theother -- with NGC 4889. It is argued that these subgroups are galaxyassociations, i.e. galactic dynamical entities moving within the maincluster. Thus, we conclude that the non-stationarity of the dynamicalprocesses ongoing in the Coma core is due to the merging of small-scalegalaxy associations, rather than of two equal sized clusters. We providethe lists of the galaxies of the associations, the observational studyof which can be of particular interest.
| 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.
| 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.
| The Globular Cluster Systems in the Coma Ellipticals. II. Metallicity Distribution and Radial Structure in NGC 4874 and Implications for Galaxy Formation
Deep Hubble Space Telescope WFPC2 images in V and I are used toinvestigate the globular cluster system (GCS) in NGC 4874, the centralcD galaxy of the Coma cluster. Although the luminosity function of theclusters displays its normal Gaussian-like shape and turnover level,other features of the system are surprising. We find the GCS to be (a)spatially extended, with core radius rc~22 kpc, (b) entirelymetal poor (a narrow, unimodal metallicity distribution with<[Fe/H]>~-1.5), and (c) modestly populated for a cD-type galaxy,with specific frequency SN=3.7+/-0.5. Model interpretationssuggest to us that as much as half of this galaxy might have accretedfrom low-mass satellites, but no single one of the three classic modesof galaxy formation (accretion, disk mergers, in situ formation) cansupply a fully satisfactory model for the formation of NGC 4874. Evenwhen they are used in combination, strong challenges to these modelsremain. We suggest that the principal anomaly in this GCS is essentiallythe complete lack of metal-rich clusters. If these were present innormal (M87-like) numbers in addition to the metal-poor ones that arealready there, then the GCS in total would more closely resemble what wesee in many other giant E galaxies. This supergiant galaxy appears tohave avoided forming globular clusters during the main metal-rich stageof star formation that built the bulk of the galaxy. Based onobservations with the NASA/ESA Hubble Space Telescope, obtained at theSpace Telescope Science Institute, which is operated by the Associationof Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
| 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
| Gravo-thermal properties and formation of elliptical galaxies
We have analyzed a sample of galaxies belonging to three clusters: Coma,Abell 85, and Abell 496 (real galaxies) and a sample of simulatedelliptical galaxies formed in a hierarchical merging scheme (virtualgalaxies). We use the Sérsic law to describe their light profile.The specific entropy (Boltzmann-Gibbs definition) is then calculatedsupposing that the galaxies behave as spherical, isotropic,one-component systems. We find that, to a good approximation ( ~ 10%),both real and virtual galaxies have an almost unique specific entropy.Within this approximation the galaxies are distributed in a thin planein the space defined by the three Sérsic law parameters, which wecall the Entropic Plane. A further analysis shows that both real andvirtual galaxies are in fact located on a thin line, thereforeindicating the existence of another - and yet unknown - physicalproperty, besides the uniqueness of the specific entropy. A more carefulexamination of the virtual galaxies sample indicates a very smallincrease of their specific entropy with merging generation. In ahierarchical scenario, this implies a correlation between the specificentropy and the total mass, which is indeed seen in our data. Thescatter and tilt of the Entropic Line, defined by Lima Neto et al.(1999a), are reduced when this correlation is taken into account.Although one cannot distinguish between various generations for realgalaxies, the distribution of their specific entropy is similar to thatin the virtual sample, suggesting that hierarchical merging processescould be an important mechanism in the building of elliptical galaxies.Based on observations collected at the Canada France Hawaii Telescopeand at the European Southern Observatory, La Silla, Chile
| 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
| The specific entropy of elliptical galaxies: an explanation for profile-shape distance indicators?
Dynamical systems in equilibrium have a stationary entropy; we suggestthat elliptical galaxies, as stellar systems in a stage ofquasi-equilibrium, may have in principle a unique specific entropy. Thisuniqueness, a priori unknown, should be reflected in correlationsbetween the fundamental parameters describing the mass (light)distribution in galaxies. Following recent photometrical work onelliptical galaxies by Caon et al., Graham & Colless and Prugniel& Simien, we use the Sérsic law to describe the light profileand an analytical approximation to its three-dimensional deprojection.The specific entropy is then calculated, supposing that the galaxybehaves as a spherical, isotropic, one-component system in hydrostaticequilibrium, obeying the ideal-gas equations of state. We predict arelation between the three parameters of the Sérsic law linked tothe specific entropy, defining a surface in the parameter space, an`Entropic Plane', by analogy with the well-known Fundamental Plane. Wehave analysed elliptical galaxies in two rich clusters of galaxies (Comaand ABCG 85) and a group of galaxies (associated with NGC 4839, nearComa). We show that, for a given cluster, the galaxies follow closely arelation predicted by the constant specific entropy hypothesis with atypical dispersion (one standard deviation) of 9.5per cent around themean value of the specific entropy. Moreover, assuming that the specificentropy is also the same for galaxies of different clusters, we are ableto derive relative distances between Coma, ABGC 85, and the group of NGC4839. If the errors are due only to the determination of the specificentropy (about 10per cent), then the error in the relative distancedetermination should be less than 20per cent for rich clusters. Wesuggest that the unique specific entropy may provide a physicalexplanation for the distance indicators based on the Sérsicprofile put forward by Young & Currie and recently discussed byBinggeli & Jerjen.
| 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.
| The near-infrared Fundamental Plane of elliptical galaxies
Near-infrared (2.2 μm) observations of a sample of 48 ellipticalgalaxies in the Coma cluster have been carried out and used to study thenear-infrared Fundamental Plane (FP) of ellipticals in this cluster. Anrms scatter of 0.072 dex is found for this relation, similar to that ofits optical counterpart, using the same sample of galaxies. Thiscorresponds to an uncertainty of 18 per cent in distances to individualgalaxies derived from this relation. The sensitivity of thenear-infrared FP to the star formation or changes in metallicity andstellar population among the ellipticals is explored and found to besmall, although a likely source of scatter in this relation iscontributions from the asymptotic giant branch (AGB) population to thenear-infrared light. Allowing for observational uncertainties, we findan intrinsic scatter of 0.060 dex in the near-infrared FP. The clustergalaxies presented here provide the zero-point for the peculiar velocitystudies, using the near-infrared FP. Changes in the slopes of theD-sigma and L-sigma relations of ellipticals between the optical andnear-infrared wavelengths are investigated and found to be due tovariations in metallicity or age (or a combination of them). However, itis not possible to disentangle the effects of age and metallicity inthese relations. We find M/L~M^alpha with alpha=0.18+/-0.01 in thenear-infrared and alpha=0.23+/-0.01 at optical wavelengths, using thesame sample of galaxies. This relation is interpreted as being due to amass-metallicity effect or changes in age or the initial mass functionslope with mass. Using evolutionary population synthesis models, we findthat the effects of age and metallicity decouple in the (M/L)_K versusMg_2 and (M/L)_K versus (V-K) diagrams. The models suggest that theobserved trends in these relations may be due to an age sequence, whilemetallicity mainly contributes to the scatter.
| Fundamental plane distances to early-type field galaxies in the South Equatorial Strip. I. The spectroscopic data
Radial velocities and central velocity dispersions are derived for 238E/S0 galaxies from medium-resolution spectroscopy. New spectroscopicdata have been obtained as part of a study of the Fundamental Planedistances and peculiar motions of early-type galaxies in three selecteddirections of the South Equatorial Strip, undertaken in order toinvestigate the reality of large-scale streaming motion; results of thisstudy have been reported in Müller et al. (1998). The new APM SouthEquatorial Strip Catalog (-17fdg 5 < delta < +2fdg 5) was used toselect the sample of field galaxies in three directions: (1) 15h10 -16h10; (2) 20h30 - 21h50; (3) 00h10 - 01h30. The spectra obtained have amedian S/N per Å of 23, an instrumental resolution (FWHM) of ~ 4Å, and the spectrograph resolution (dispersion) is ~ 100 kms-1. The Fourier cross-correlation method was used to derivethe radial velocities and velocity dispersions. The velocity dispersionshave been corrected for the size of the aperture and for the galaxyeffective radius. Comparisons of the derived radial velocities with datafrom the literature show that our values are accurate to 40 kms-1. A comparison with results from Jo rgensen et al. (1995)shows that the derived central velocity dispersion have an rms scatterof 0.036 in log sigma . There is no offset relative to the velocitydispersions of Davies et al. (1987).
| The tilt of the Fundamental Plane of early-type galaxies: wavelength dependence
The photometric parameters R_e and mu_e of 74 early-type (E+S0+S0a)galaxies within 2 deg projected radius from the Coma cluster centre arederived for the first time in the near-infrared H band (1.65 μm).These are used, coupled with measurements of the central velocitydispersion sigma found in the literature, to determine the H-bandFundamental Plane (FP) relation of this cluster: logR_e~Alogsigma+bmu_e. The same procedure is applied to previouslyavailable photometric data in the BVrIK bands, to perform amultiwavelength study of the FP relation. Because systematicuncertainties in the value of the FP parameters are introduced both bythe choice of the fitting algorithm used to derive the FP template, andby the presence of statistical biases connected with the sampleselection procedure, we emphasize the importance of deriving the FPparameters in the six different photometric bands using an identicalfitting algorithm, and appropriate corrections to eliminate the effectsof sample incompleteness. Once these corrections are applied, we findthat the FP b coefficient is stable with wavelength (~0.35+/-0.02),while the A coefficient increases significantly with increasingwavelength: from ~1.35 to ~1.70 (+/-0.1) from the optical to theinfrared, in agreement with an earlier result presented recently byPahre and Djorgovski. Therefore the slope of the FP relation, althoughchanging with wavelength, never approaches the virial theoremexpectation A=2.0 when the central velocity dispersion only is used tobuild the FP. We also find that the magnitude of the slope change can beentirely explained by the presence of the well-known relation betweencolour and magnitude among early-type galaxies. We conclude that thetilt of the Fundamental Plane is significant, and must be the result ofsome form of broken homology among early-type galaxies, while itswavelength dependence derives from whatever mechanism (currently thepreferred one is the existence of a mass-metal content sequence)produces the colour-magnitude relation in those galaxies.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
Каталог и designations:
|
