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The Ages of Elliptical Galaxies from Infrared Spectral Energy Distributions
The mean ages of early-type galaxies obtained from the analysis ofoptical spectra give a mean age of 8 Gyr at z=0, with 40% being youngerthan 6 Gyr. Independent age determinations are possible by usinginfrared spectra (5-21 μm), which we have obtained with the InfraredSpectrograph on Spitzer. This age indicator is based on the collectivemass-loss rate of stars, in which mass loss from AGB stars produces asilicate emission feature at 9-12 μm. This feature decreases morerapidly than the shorter wavelength continuum as a stellar populationages, providing an age indicator. From observations of 30 nearbyearly-type galaxies, 29 show a spectral energy distribution dominated bystars, and one has significant emission from the ISM and is excluded.The infrared age indicators for the 29 galaxies show them all to be old,with a mean age of about 10 Gyr and a standard deviation of only a fewGyr. This is consistent with the ages inferred from the values ofM/LB, but is inconsistent with the ages derived from theoptical line indices, which can be much younger. All of these ageindicators are luminosity weighted and should be correlated, even ifmultiple-age components are considered. The inconsistency indicates thatthere is a significant problem with either the infrared and theM/LB ages, which agree, or with the ages inferred from theoptical absorption lines.
| Infrared Surface Brightness Fluctuations of Magellanic Star Clusters
We present surface brightness fluctuations (SBFs) in the near-IR for 191Magellanic star clusters available in the Second Incremental and All SkyData releases of the Two Micron All Sky Survey (2MASS) and compare themwith SBFs of Fornax Cluster galaxies and with predictions from stellarpopulation models as well. We also construct color-magnitude diagrams(CMDs) for these clusters using the 2MASS Point Source Catalog (PSC).Our goals are twofold. The first is to provide an empirical calibrationof near-IR SBFs, given that existing stellar population synthesis modelsare particularly discrepant in the near-IR. Second, whereas mostprevious SBF studies have focused on old, metal-rich populations, thisis the first application to a system with such a wide range of ages(~106 to more than 1010 yr, i.e., 4 orders ofmagnitude), at the same time that the clusters have a very narrow rangeof metallicities (Z~0.0006-0.01, i.e., 1 order of magnitude only). Sincestellar population synthesis models predict a more complex sensitivityof SBFs to metallicity and age in the near-IR than in the optical, thisanalysis offers a unique way of disentangling the effects of age andmetallicity. We find a satisfactory agreement between models and data.We also confirm that near-IR fluctuations and fluctuation colors aremostly driven by age in the Magellanic cluster populations and that inthis respect they constitute a sequence in which the Fornax Clustergalaxies fit adequately. Fluctuations are powered by red supergiantswith high-mass precursors in young populations and by intermediate-massstars populating the asymptotic giant branch in intermediate-agepopulations. For old populations, the trend with age of both fluctuationmagnitudes and colors can be explained straightforwardly by evolution inthe structure and morphology of the red giant branch. Moreover,fluctuation colors display a tendency to redden with age that can befitted by a straight line. For the star clusters only,(H-Ks)=(0.21+/-0.03)log(age)-(1.29+/-0.22) once galaxies areincluded, (H-Ks)=(0.20+/-0.02)log(age)-(1.25+/-0.16).Finally, we use for the first time a Poissonian approach to establishthe error bars of fluctuation measurements, instead of the customaryMonte Carlo simulations.This research has made use of the NASA/ IPAC Infrared Science Archive,which is operated by the Jet Propulsion Laboratory, California Instituteof Technology, under contract with the National Aeronautics and SpaceAdministration.
| Peculiarities and populations in elliptical galaxies. I. An old question revisited
Morphological peculiarities, as defined from isophote asymmetries andnumber of detected shells, jets or similar features, have been estimatedin a sample of 117 E classified galaxies, and qualified by an ad hocΣ2 index. The overall frequency of ``peculiar'' objects(Pec subsample) is 32.5%. It decreases with the cosmic density of theenvironment, being minimal for the Virgo cluster, the densestenvironment in the sampled volume. This environmental effect is strongerfor galaxies with relatively large Σ2.The Pec subsample objects are compared with ``normal'' objects (Nopsubsample) as regards their basic properties. Firstly, theysystematically deviate from the Fundamental Plane and the Faber-Jacksonrelation derived for the Nop subsample, being too bright for their mass.Secondly, the dust content of galaxies, as estimated from IRAS fluxes,are similar in both subsamples. Third, the same is true of the frequencyof Kinematically Distinct cores (KDC), suggesting that KDC andmorphological peculiarities do not result from the same events in thehistory of E-galaxies.Using the Nop sample alone, we obtain very tight reference relationsbetween stellar population indicators (U-B, B-V, B-R, V-I,Mg2, Hβ, , Mgb) and the central velocitydispersion σ0. The discussion of the residuals of theserelations allows us to classify the Pec galaxies in two families i.e.the YP or NGC 2865 family, and the NP or NGC 3923 one. Galaxies in thefirst group show consistent evidence for a younger stellar populationmixed with the old one, in agreement with classical results (Schweizeret al. \cite{Schweizer1990}; Schweizer & Seitzer\cite{Schweizer1992}). The second group, however, has ``normal``, orreddish, populations. It is remarkable that a fraction (circa 40%) ofmorphologically perturbed objects do not display any signature of ayoung population, either because the event responsible for thepecularity is too ancient, or because it did not produce significantstar formation (or eventually that the young sub-population has highmetallicity).A preliminary attempt is made to interpret the populations of Pecobjects by combining a young Single Stellar Population with a Nopgalaxy, with only limited success, perhaps largely due to uncertaintiesin the SSP indices used.Based in part on observations collected at the Observatoire deHaute-Provence.Figures \ref{fig1}-\ref{fig3} are only available in electronic form athttp://www.edpsciences.orgTable 10 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/423/833
| Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations
To empirically calibrate the IR surface brightness fluctuation (SBF)distance scale and probe the properties of unresolved stellarpopulations, we measured fluctuations in 65 galaxies using NICMOS on theHubble Space Telescope. The early-type galaxies in this sample includeelliptical and S0 galaxies and spiral bulges in a variety ofenvironments. Absolute fluctuation magnitudes in the F160W (1.6 μm)filter (MF160W) were derived for each galaxy using previouslymeasured I-band SBF and Cepheid variable star distances. F160W SBFs canbe used to measure distances to early-type galaxies with a relativeaccuracy of ~10%, provided that the galaxy color is known to ~0.035 magor better. Near-IR fluctuations can also reveal the properties of themost luminous stellar populations in galaxies. Comparison of F160Wfluctuation magnitudes and optical colors to stellar population modelpredictions suggests that bluer elliptical and S0 galaxies havesignificantly younger populations than redder ones and may also be moremetal-rich. There are no galaxies in this sample with fluctuationmagnitudes consistent with old, metal-poor (t>5 Gyr, [Fe/H]<-0.7)stellar population models. Composite stellar population models implythat bright fluctuations in the bluer galaxies may be the result of anepisode of recent star formation in a fraction of the total mass of agalaxy. Age estimates from the F160W fluctuation magnitudes areconsistent with those measured using the Hβ Balmer-line index. Thetwo types of measurements make use of completely different techniquesand are sensitive to stars in different evolutionary phases. Bothtechniques reveal the presence of intermediate-age stars in theearly-type galaxies of this sample.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by AURA,Inc., under NASA contract NAS 5-26555.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| 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.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| Surface brightness fluctuation distances for dwarf elliptical galaxies in the Fornax cluster
We have obtained deep B and R-band CCD images of eight dwarf elliptical(dE) galaxies in the Fornax cluster using the FORS1 instrument at theVLT in service mode under excellent atmospheric conditions. A total of92 fields distributed over the central regions of the galaxies have beenanalysed to measure local (B-R)0 colours and R-band surfacebrightness fluctuation (SBF) magnitudes /line{m}R. Within agalaxy the observed correlation of (B-R)0 with/line{m}R0 follows closely the predicted slope ofthe colour-fluctuation luminosity relation for composite single-burst,mainly old, metal-poor stellar populations. This allows to determine thedistances of the dEs from simple offset measurements to a typically 9%accuracy. The distance distribution of these genuine cluster dwarfscenters at a mean distance of (m-M)0=31.54+/-0.07 mag, or20.3 +/- 0.7 Mpc, a value that is in best agreement with previous SBFwork on Fornax early-type giants and thus represents a robust estimateof the distance to the Fornax cluster core. The application of thebootstrap resampling technique on the distance data further reveals acluster depth of sigmaint = 1.4{+0.5 atop -0.8} Mpc. We takethis preliminary result as a confirmation of the compact appearance ofFornax in the projection on the sky although the cluster might beslightly more elongated along the line of sight. Combining the newlyderived cluster distance with the cosmological velocity of Fornax of1324+/-41 km s-1 gives a Hubble constant of H0 =65 +/- 4 km s-1 Mpc-1. This value is consistent atthe 95% confidence level with both the most recent result from the teamthat favours a long distance scale and the final value adopted by theHST ``Key Project'' team in their work for the Hubble constant. Finally,we explore the possibility to determine rough metallicities of ourcluster dEs from their (B-R)0 colours via Worthey's stellarpopulation synthesis models. The median metallicities are found in therange from -1.5 to -1 with a concentration around [Fe/H] =-1. Acomparison with spectral line indices results available for threegalaxies shows good agreement. Moreover, the derived metallicities placethe bright Fornax dEs on the extension of the metallicity-luminosityrelation defined by the low luminous Local Group dEs which providesadditional support for the (B-R)0 colour as a usefulmetallicity estimator. The data further suggest an age range between 10and 12 Gyr for the Fornax dwarfs.Based on observations collected at the European Southern Observatory(ESO 68.A-0176).
| Early-type galaxies in low-density environments
We describe the construction and study of an objectively defined sampleof early-type galaxies in low-density environments. The sample galaxiesare selected from a recently completed redshift survey using uniform andreadily quantified isolation criteria, and are drawn from a sky area of~700 deg2, to a depth of 7000 km s-1 and anapparent magnitude limit of bJ<= 16.1. Their early-type(E/S0) morphologies are confirmed by subsequent CCD imaging. Five out ofthe nine sample galaxies show signs of morphological peculiarity such astidal debris or blue circumnuclear rings. We confirm that E/S0 galaxiesare rare in low-density regions, accounting for only ~8 per cent of thetotal galaxy population in such environments. We present spectroscopicobservations of nine galaxies in the sample, which are used, inconjunction with updated stellar population models, to investigate starformation histories. Our line-strength analysis is conducted at therelatively high spectral resolution of 4.1 Å. Environmentaleffects on early-type galaxy evolution are investigated by comparisonwith a sample of Fornax cluster E/S0s (identically analysed). Resultsfrom both samples are compared with predictions from semi-analyticgalaxy formation models. From the strength of [OII]λ3727 emissionwe infer only a low level of ongoing star formation (<0.15Msolar yr-1). Relative to the Fornax sample, alarger fraction of the galaxies exhibit [OIII]λ5007 nebularemission and, where present, these lines are slightly stronger thantypical for cluster E/S0s. The Mg-σ relation of E/S0s inlow-density regions is shown to be indistinguishable from that of theFornax sample. Luminosity-weighted stellar ages and metallicities aredetermined by considering various combinations of line-indices; inparticular the HγF versus Fe5015 diagram cleanlyresolves the age-metallicity degeneracy at the spectral resolution ofour analysis. At a given luminosity, the E/S0 galaxies in low-densityregions are younger than the E/S0s in clusters (by ~2-3 Gyr), and alsomore metal-rich (by ~0.2 dex). We infer that an anti-correlation of ageand metallicity effects is responsible for maintaining the zero-point ofthe Mg-σ relation. The youngest galaxies in our sample show clearmorphological signs of interaction. The lower mean age of our sample,relative to cluster samples, confirms, at least qualitatively, a robustprediction of hierarchical galaxy formation models. By contrast, theenhanced metallicity in the field is contrary to the predictions andhighlights shortcomings in the detailed treatment of star formationprocesses in current models. The [Mg/Fe] abundance ratio appears to spana similar, mostly super-solar, range both in low-density regions and inFornax cluster galaxies. This result is quite unexpected in simplehierarchical models.
| The `Photometric Plane' of elliptical galaxies
The Sérsic (r1/n) index n of an elliptical galaxy (orbulge) has recently been shown to correlate strongly (r= 0.8) with thecentral velocity dispersion of a galaxy. This index could thereforeprove extremely useful and cost-effective (in terms of both telescopetime and data reduction) for many fields of extragalactic research. Itis a purely photometric quantity which apparently not only traces themass of a bulge but has additionally been shown to reflect the degree ofbulge concentration. This paper explores the affect of replacing thecentral velocity dispersion term in the Fundamental Plane with theSérsic index n. Using a sample of early-type galaxies from theVirgo and Fornax clusters, various (B-band) `Photometric Planes' wereconstructed and found to have a scatter of 0.14-0.17 dex in logre, or a distance error of 38-48 per cent per galaxy (thehigher values arising from the inclusion of the S0 galaxies). Thecorresponding Fundamental Plane yielded a 33-37 per cent error indistance for the same galaxy samples (i.e. ~15-30 per cent lessscatter). The gains in using a hyperplane (i.e. adding the Sérsicindex to the Fundamental Plane as a fourth parameter) were small, givinga 27-33 per cent error in distance, depending on the galaxy sample used.The Photometric Plane has been used here to estimate the Virgo-Fornaxdistance modulus; giving a value of 0.62 +/- 0.30 mag[cf. 0.51 +/- 0.21,Hubble Space Telescope (HST) Key Project on the Extragalactic DistanceScale]. The prospects for using the Photometric Plane at higherredshifts appears promising. Using published data on the intermediateredshift cluster Cl 1358 + 62 (z= 0.33) gave a Photometric Planedistance error of 35-41 per cent per galaxy.
| 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.
| Surface Brightness Fluctuations of Fornax Cluster Galaxies: Calibration of Infrared Surface Brightness Fluctuations and Evidence for Recent Star Formation
We have measured KS-band (2.0-2.3 μm) surface brightnessfluctuations (SBFs) of 19 early-type galaxies in the Fornax Cluster.Fornax is ideally suited both for calibrating SBFs as distanceindicators and for using SBFs to probe the unresolved stellar content ofearly-type galaxies. Combining our results with published data for othernearby clusters, we calibrate KS-band SBFs using Hubble SpaceTelescope (HST) Cepheid cluster distances and I-band SBF distances toindividual galaxies. With the latter, the resulting calibrationisMKS=(-5.84+/-0.04)+(3.6+/-0.8)[(V-Ic)0-1.15],valid for1.05<(V-Ic)0<1.25 and not including anysystematic errors in the HST Cepheid distance scale. The fit accountsfor the covariance between V-Ic and MKSwhen calibrated in this fashion. The intrinsic cosmic scatter ofMKS appears to be larger than that of I-band SBFs.S0 galaxies may follow a different relation, although the data areinconclusive. The discovery of correlation between KS-bandfluctuation magnitudes and colors with V-Ic is a new clueinto the star formation histories of early-type galaxies. This relationnaturally accounts for galaxies previously claimed to have anomalouslybright K-band SBFs, namely, M32 and NGC 4489. Models indicate that thestellar populations dominating the SBF signal have a significant rangein age; some scatter in metallicity may also be present. The youngestages imply some galaxies have very luminous giant branches, akin tothose in intermediate-age (few Gyr) Magellanic Cloud clusters. Theinferred metallicities are roughly solar, although this depends on thechoice of theoretical models. A few Fornax galaxies have unusuallybright KS-band SBFs, perhaps originating from ahigh-metallicity burst of star formation in the last few Gyr. Theincreased spread and brightening of the KS-band SBFs withbluer V-Ic suggest that the lower mass cluster galaxies(<~0.1L*) may have had more extended and more heterogeneous starformation histories than those of the more massive galaxies.
| 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.
| Line-strength indices and velocity dispersions for 148 early-type galaxies in different environments
We have derived high quality line-strength indices and velocitydispersions for a sample of 148 early-type galaxies in differentenvironments. The wavelength region covered by the observations (lambda=~ 4600 to 6600 Å) includes the Lick/IDS indices Hβ,Mg1, Mg2, Mgb, Fe5015, Fe5270, Fe5335, Fe5406,Fe5709, Fe5782, NaD, TiO1 and TiO2. The data areintended to address possible differences of the stellar populations ofearly-type galaxies in low- and high-density environments. This paperdescribes the sample properties, explains the data reduction andpresents the complete list of all the measurements. Most galaxies of thesample (85%) had no previous measurements of any Lick/IDS indices andfor 30% of the galaxies we present first-time determinations of theirvelocity dispersions. Special care is taken to identify galaxies withemission lines. We found that 62 per cent of the galaxies in the samplehave emission lines, as measured by the equivalent width of the [OIII]5007Å line, EW[OIII] > 0.3 Å. Tables 5 and 6 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/ A+A/395/431. They are also available via ftp atftp.mpe.mpg.de in the directory people/dthomas/Beuing02 or via WWW atftp://ftp.mpe.mpg.de/people/dthomas/Beuing02.
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| A synthesis of data from fundamental plane and surface brightness fluctuation surveys
We perform a series of comparisons between distance-independentphotometric and spectroscopic properties used in the surface brightnessfluctuation (SBF) and fundamental plane (FP) methods of early-typegalaxy distance estimation. The data are taken from two recent surveys:the SBF Survey of Galaxy Distances and the Streaming Motions of AbellClusters (SMAC) FP survey. We derive a relation between(V-I)0 colour and Mg2 index using nearly 200galaxies and discuss implications for Galactic extinction estimates andearly-type galaxy stellar populations. We find that the reddenings fromSchlegel et al. for galaxies with E(B-V)>~0.2mag appear to beoverestimated by 5-10 per cent, but we do not find significant evidencefor large-scale dipole errors in the extinction map. In comparison withstellar population models having solar elemental abundance ratios, thegalaxies in our sample are generally too blue at a given Mg2;we ascribe this to the well-known enhancement of the α-elements inluminous early-type galaxies. We confirm a tight relation betweenstellar velocity dispersion σ and the SBF `fluctuation count'parameter N, which is a luminosity-weighted measure of the total numberof stars in a galaxy. The correlation between N and σ is eventighter than that between Mg2 and σ. Finally, we deriveFP photometric parameters for 280 galaxies from the SBF survey data set.Comparisons with external sources allow us to estimate the errors onthese parameters and derive the correction necessary to bring them on tothe SMAC system. The data are used in a forthcoming paper, whichcompares the distances derived from the FP and SBF methods.
| 2D modelling of the light distribution of early-type galaxies in a volume-limited sample - II. Results for real galaxies
In this paper we analyse the results of the two-dimensional (2D) fit ofthe light distribution of 73 early-type galaxies belonging to the Virgoand Fornax clusters, a sample volume- and magnitude-limited down toMB=-17.3, and highly homogeneous. In our previous paper(Paper I) we have presented the adopted 2D models of thesurface-brightness distribution - namely the r1/n and(r1/n+exp) models - we have discussed the main sources oferror affecting the structural parameters, and we have tested theability of the chosen minimization algorithm (MINUIT) in determining thefitting parameters using a sample of artificial galaxies. We show that,with the exception of 11 low-luminosity E galaxies, the best fit of thereal galaxy sample is always achieved with the two-component(r1/n+exp) model. The improvement in the χ2due to the addition of the exponential component is found to bestatistically significant. The best fit is obtained with the exponent nof the generalized r1/n Sersic law different from theclassical de Vaucouleurs value of 4. Nearly 42 per cent of the samplehave n<2, suggesting the presence of exponential `bulges' also inearly-type galaxies. 20 luminous E galaxies are fitted by thetwo-component model, with a small central exponential structure (`disc')and an outer big spheroid with n>4. We believe that this is probablydue to their resolved core. The resulting scalelengths Rh andRe of each component peak approximately at ~1 and ~2kpc,respectively, although with different variances in their distributions.The ratio Re/Rh peaks at ~0.5, a value typical fornormal lenticular galaxies. The first component, represented by ther1/n law, is probably made of two distinct families,`ordinary' and `bright', on the basis of their distribution in theμe-log(Re) plane, a result already suggested byCapaccioli, Caon and D'Onofrio. The bulges of spirals and S0 galaxiesbelong to the `ordinary' family, while the large spheroids of luminous Egalaxies form the `bright' family. The second component, represented bythe exponential law, also shows a wide distribution in theμ0c-log(Rh) plane. Small discs (orcores) have short scalelengths and high central surface brightness,while normal lenticulars and spiral galaxies generally have scalelengthshigher than 0.5kpc and central surface brightness brighter than20magarcsec-2 (in the B band). The scalelengths Reand Rh of the `bulge' and `disc' components are probablycorrelated, indicating that a self-regulating mechanism of galaxyformation may be at work. Alternatively, two regions of theRe-Rh plane are avoided by galaxies due todynamical instability effects. The bulge-to-disc (B/D) ratio seems tovary uniformly along the Hubble sequence, going from late-type spiralsto E galaxies. At the end of the sequence the ratio between the largespheroidal component and the small inner core can reach B/D~100.
| Cold gas in elliptical galaxies
We explore the evolution of the cold gas (molecular and neutralhydrogen) of elliptical galaxies and merger remnants ordered into a timesequence on the basis of spectroscopic age estimates. We find that thefraction of cold gas in early merger remnants decreases significantlyfor ~1-2Gyr, but subsequent evolution toward evolved elliptical systemssees very little change. This trend can be attributed to an initial gasdepletion by strong star formation, which subsequently declines toquiescent rates. This explanation is consistent with the merger picturefor the formation of elliptical galaxies. We also explore the relationbetween the HI-to-H2 mass ratio and spectroscopic galaxy age,but find no evidence for a statistically significant trend. Thissuggests little net HI-to-H2 conversion for the systems inthe present sample.
| Structural evolution in elliptical galaxies: the age-shape relation
We test the hypothesis that the apparent axial ratio of an ellipticalgalaxy is correlated with the age of its stellar population. We findthat old ellipticals (with estimated ages t>7.5Gyr) are rounder onaverage than younger ellipticals. The statistical significance of thisshape difference is greatest at small radii; a Kolmogorov-Smirnov testcomparing the axial ratios of the two populations at R=Re/16yields a statistical significance greater than 99.96 per cent. Therelation between age and apparent shape is linked to the core/power-lawsurface brightness profile dichotomy. Core ellipticals have olderstellar populations, on average, than power-law ellipticals and arerounder in their inner regions. Our findings are consistent with ascenario in which power-law ellipticals are formed in gas-rich mergers,while core ellipticals form in dissipationless mergers, with coresformed and maintained by the influence of a binary black hole.
| The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances
We report data for I-band surface brightness fluctuation (SBF)magnitudes, (V-I) colors, and distance moduli for 300 galaxies. Thesurvey contains E, S0, and early-type spiral galaxies in the proportionsof 49:42:9 and is essentially complete for E galaxies to Hubblevelocities of 2000 km s-1, with a substantial sampling of Egalaxies out to 4000 km s-1. The median error in distancemodulus is 0.22 mag. We also present two new results from the survey.(1) We compare the mean peculiar flow velocity (bulk flow) implied byour distances with predictions of typical cold dark matter transferfunctions as a function of scale, and we find very good agreement withcold, dark matter cosmologies if the transfer function scale parameterΓ and the power spectrum normalization σ8 arerelated by σ8Γ-0.5~2+/-0.5. Deriveddirectly from velocities, this result is independent of the distributionof galaxies or models for biasing. This modest bulk flow contradictsreports of large-scale, large-amplitude flows in the ~200 Mpc diametervolume surrounding our survey volume. (2) We present adistance-independent measure of absolute galaxy luminosity, N and showhow it correlates with galaxy properties such as color and velocitydispersion, demonstrating its utility for measuring galaxy distancesthrough large and unknown extinction. Observations in part from theMichigan-Dartmouth-MIT (MDM) Observatory.
| Dusty Nuclear Disks and Filaments in Early-Type Galaxies
We examine the dust properties of a nearby distance-limited sample ofearly-type galaxies using WFPC2 of the Hubble Space Telescope. Dust isdetected in 29 out of 67 galaxies (43%), including 12 with small nucleardusty disks. In a separate sample of 40 galaxies biased for thedetection of dust by virtue of their detection in IRAS 100 μm band,dust is found in ~78% of the galaxies, 15 of which contain dusty disks.In those galaxies with detectable dust, the apparent mass of the dustcorrelates with radio and far-infrared luminosity, becoming moresignificant for systems with filamentary dust. A majority of IRAS andradio detections are also associated with dusty galaxies rather thandustless galaxies. This indicates that thermal emission from clumpy,filamentary dust is the main source of the far-IR radiation inearly-type galaxies. Dust in small disklike morphology tends to be wellaligned with the major axis of the host galaxies, while filamentary dustappears to be more randomly distributed with no preference for alignmentwith any major galactic structure. This suggests that, if the dustydisks and filaments have a common origin, the dust originates externallyand requires time to dynamically relax and settle in the galaxypotential in the form of compact disks. More galaxies with visible dustthan without dust display emission lines, indicative of ionized gas,although such nuclear activity does not show a preference for dusty diskover filamentary dust. There appears to be a weak relationship betweenthe mass of the dusty disks and central velocity dispersion of thegalaxy, suggesting a connection with a similar recently recognizedrelationship between the latter and the black hole mass. 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 contractNAS5-26555.
| The neutral hydrogen content of Fornax cluster galaxies
We present a new set of deep H I observations of member galaxies of theFornax cluster. We detected 35 cluster galaxies in HI. The resulting sample, the most comprehensive to date, is used toinvestigate the distribution of neutral hydrogen in the clustergalaxies. We compare the H I content of the detected cluster galaxieswith that of field galaxies by measuring H I mass-to-light ratios andthe H I deficiency parameter of Solanes et al. (\cite{Sol96}). The meanH I mass-to-light ratio of the cluster galaxies is 0.68+/- 0.15,significantly lower than for a sample of H I-selected field galaxies(1.15+/- 0.10), although not as low as in the Virgocluster (0.45+/- 0.03). In addition, the H I content of twocluster galaxies (NGC 1316C and NGC1326B) appears to have been affected by interactions. The meanH I deficiency for the cluster is 0.38+/-0.09 (for galaxy types T=1-6),significantly greater than for the field sample (0.05+/-0.03). Boththese tests show that Fornax cluster galaxies are HI-deficient compared to field galaxies. The kinematics of the clustergalaxies suggests that the H I deficiency may be caused by ram-pressurestripping of galaxies on orbits that pass close to the cluster core. Wealso derive the most complete B-band Tully - Fisher relation of inclinedspiral galaxies in Fornax. A subcluster in theSouth-West of the main cluster contributes considerably to the scatter.The scatter for galaxies in the main cluster alone is 0.50 mag, which isslightly larger than the intrinsic scatter of 0.4 mag. We use the Tully- Fisher relation to derive a distance modulus ofFornax relative to the Virgocluster of -0.38+/- 0.14 mag. The galaxies in the subclusterare (1.0+/-0.5) mag brighter than the galaxies of the main cluster,indicating that they are situated in the foreground. With their meanvelocity 95 km s-1 higher than that of the main cluster weconclude that the subcluster is falling into the main Fornaxcluster.
| The stellar populations of early-type galaxies in the Fornax cluster
We have measured central line strengths for a magnitude-limited sampleof early-type galaxies in the Fornax cluster, comprising 11 elliptical(E) and 11 lenticular (S0) galaxies, more luminous thanMB=-17. When compared with single-burst stellar populationmodels we find that the centres of Fornax ellipticals follow a locus offixed age and have metallicities varying roughly from half solar totwice solar. The centres of (lower luminosity) lenticular galaxies,however, exhibit a substantial spread to younger luminosity-weightedages, indicating a more extended star formation history. Galaxies withold stellar populations show tight scaling relations between metal-lineindices and the central velocity dispersion. Remarkably also, the Felines are well correlated with σ0. Our detailedanalysis of the stellar populations suggests that these scalingrelations are driven mostly by metallicity. Galaxies with a youngstellar component do generally deviate from the main relation. Inparticular, the lower luminosity S0s show a large spread. Ourconclusions are based on several age/metallicity diagnostic diagrams inthe Lick/IDS system comprising established indices such asMg2 and Hβ as well as new and more sensitive indicessuch as HγA and Fe3, a combination of three prominentFe lines. The inferred difference in the age distribution betweenlenticular and elliptical galaxies is a robust conclusion, as the modelsgenerate consistent relative ages using different age and metallicityindicators, even though the absolute ages remain uncertain. The absoluteage uncertainty is mainly caused by the effects of non-solar abundanceratios which are not yet accounted for by the stellar population models.Furthermore, we find that elliptical galaxies and the bulge of onebright S0 are overabundant in magnesium, where the most luminousgalaxies show the strongest overabundances. The stellar populations ofyoung and faint S0s are consistent with solar abundance ratios or a weakMg underabundance. Two of the faintest lenticular galaxies in our samplehave blue continua and extremely strong Balmer-line absorption,suggesting star formation <2Gyr ago.
| A Database of Cepheid Distance Moduli and Tip of the Red Giant Branch, Globular Cluster Luminosity Function, Planetary Nebula Luminosity Function, and Surface Brightness Fluctuation Data Useful for Distance Determinations
We present a compilation of Cepheid distance moduli and data for foursecondary distance indicators that employ stars in the old stellarpopulations: the planetary nebula luminosity function (PNLF), theglobular cluster luminosity function (GCLF), the tip of the red giantbranch (TRGB), and the surface brightness fluctuation (SBF) method. Thedatabase includes all data published as of 1999 July 15. The mainstrength of this compilation resides in the fact that all data are on aconsistent and homogeneous system: all Cepheid distances are derivedusing the same calibration of the period-luminosity relation, thetreatment of errors is consistent for all indicators, and measurementsthat are not considered reliable are excluded. As such, the database isideal for comparing any of the distance indicators considered, or forderiving a Cepheid calibration to any secondary distance indicator, suchas the Tully-Fisher relation, the Type Ia supernovae, or the fundamentalplane for elliptical galaxies. This task has already been undertaken byFerrarese et al., Sakai et al., Kelson et al., and Gibson et al.Specifically, the database includes (1) Cepheid distances, extinctions,and metallicities; (2) reddened apparent λ5007 Å magnitudesof the PNLF cutoff; (3) reddened apparent magnitudes and colors of theturnover of the GCLF (in both the V and B bands); (4) reddened apparentmagnitudes of the TRGB (in the I band) and V-I colors at 0.5 mag fainterthan the TRGB; and (5) reddened apparent surface brightness fluctuationmagnitudes measured in Kron-Cousin I, K', andKshort, and using the F814W filter with the Hubble SpaceTelescope (HST) WFPC2. In addition, for every galaxy in the database wegive reddening estimates from IRAS/DIRBE as well as H I maps, J2000coordinates, Hubble and T-type morphological classification, apparenttotal magnitude in B, and systemic velocity.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| 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.
| The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXVII. A Derivation of the Hubble Constant Using the Fundamental Plane and Dn-σ Relations in Leo I, Virgo, and Fornax
Using published photometry and spectroscopy, we construct thefundamental plane and Dn-σ relations in Leo I, Virgo,and Fornax. The published Cepheid period-luminosity (PL) relations tospirals in these clusters fixes the relation between angular size andmetric distance for both the fundamental plane and Dn-σrelations. Using the locally calibrated fundamental plane, we inferdistances to a sample of clusters with a mean redshift of cz~6000 kms-1, and derive a value of H0=78+/-5+/-9 kms-1 Mpc-1 (random and systematic errors,respectively) for the local expansion rate. This value includes acorrection for depth effects in the Cepheid distances to the nearbyclusters, which decreased the deduced value of the expansion rate by5%+/-5%. If one further adopts the metallicity correction to the CepheidPL relation as derived by the Key Project, the value of the Hubbleconstant would decrease by a further 6%+/-4%. These two sources ofsystematic error, when combined with a +/-6% error due to theuncertainty in the distance to the Large Magellanic Cloud, a +/-4% errordue to uncertainties in the WFPC2 calibration, and several small sourcesof uncertainty in the fundamental plane analysis, yield a totalsystematic uncertainty of +/-11%. We find that the values obtained usingeither the cosmic microwave background (CMB) or a flow-field model, forthe reference frame of the distant clusters, agree to within 1%. TheDn-σ relation also produces similar results, asexpected from the correlated nature of the two scaling relations. Acomplete discussion of the sources of random and systematic error inthis determination of the Hubble constant is also given, in order tofacilitate comparison with the other secondary indicators being used bythe Key Project.
| The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXVI. The Calibration of Population II Secondary Distance Indicators and the Value of the Hubble Constant
A Cepheid-based calibration is derived for four distance indicators thatutilize stars in old stellar populations: the tip of the red giantbranch (TRGB), the planetary nebula luminosity function (PNLF), theglobular cluster luminosity function (GCLF), and the surface brightnessfluctuation method (SBF). The calibration is largely based on theCepheid distances to 18 spiral galaxies within cz=1500 km s-1obtained as part of the Hubble Space Telescope (HST) Key Project on theExtragalactic Distance Scale, but relies also on Cepheid distances fromseparate HST and ground-based efforts. The newly derived calibration ofthe SBF method is applied to obtain distances to four Abell clusters inthe velocity range 3800-5000 km s-1. Combined with clustervelocities corrected for a cosmological flow model, these distancesimply a value of the Hubble constant of H0=69+/-4(random)+/-6 (systematic) km s-1 Mpc-1. Thisresult assumes that the Cepheid PL relation is independent of themetallicity of the variable stars; adopting a metallicity correction asin Kennicutt et al. would produce a 5%+/-3% decrease in H0.Finally, the newly derived calibration allows us to investigatesystematics in the Cepheid, PNLF, SBF, GCLF, and TRGB distance scales.
| The Stellar Population Histories of Early-Type Galaxies. II. Controlling Parameters of the Stellar Populations
This paper analyzes single stellar population (SSP)-equivalentparameters for 50 local elliptical galaxies as a function of theirstructural parameters. The galaxy sample is drawn from the high-qualityspectroscopic surveys of González (1993) and Kuntschner (1998).The basic data are central values of SSP-equivalent ages, t,metallicities, [Z/H], and ``enhancement'' ratios, [E/Fe], derived inPaper I, together with global structural parameters including velocitydispersions, radii, surface brightnesses, masses, and luminosities. Thegalaxies fill a two-dimensional plane in the four-dimensional space of[Z/H], logt, logσ, and [E/Fe]. SSP age, t, and velocitydispersion, σ, can be taken as the two independent parameters thatspecify a galaxy's location in this ``hyperplane.'' The hyperplane canbe decomposed into two subrelations: (1) a ``Z-plane,'' in which [Z/H]is a linear function of logσ and logt and (2) a relation between[E/Fe] and σ in which [E/Fe] is larger in high-σ galaxies.Velocity dispersion is the only structural parameter that is found tomodulate the stellar populations; adding other structural variables suchas Ie or re does not predict [Z/H] or [E/Fe] moreaccurately. Cluster and field ellipticals follow the same hyperplane,but their (σ,t) distributions within it differ. Most Fornax andVirgo cluster galaxies are old, with a only a small sprinkling ofgalaxies to younger ages. The field ellipticals span a larger range inSSP age, with a tendency for lower σ galaxies to be younger. Thepresent sample thus suggests that the distribution of local ellipticalsin the (σ,t) plane may depend on environment. Since the(σ,t) distribution affects all two-dimensional projectionsinvolving SSP parameters, many of the familiar scaling laws attributedto ellipticals may also depend on environment. Some evidence for this isseen in the current sample. For example, only Fornax ellipticals showthe classic mass-metallicity relation, whereas other subsamples do not.The tight Mg-σ relations of these ellipticals can be understood astwo-dimensional projections of the metallicity hyperplane showing itedge-on. At fixed σ, young age tends to be offset by high [Z/H],preserving Mg nearly constant. The tightness of the Mg-σ relationsdoes not necessarily imply a narrow range of ages at fixed σ.Although SSP parameters are heavily weighted by young stars, modelingthem still places tight constraints on the total star formation historyof elliptical galaxies. The relation between [E/Fe] and σ isconsistent with a higher effective yield of Type II SNe elements athigher σ. This might occur if the IMF is enhanced in massive starsat high σ, or if more SNe II-enriched gas is retained by deepergalactic potential wells. Either way, modulating Type II yields versusσ seems to fit the data better than modulating Type Ia yields. TheZ-plane is harder to explain and may be a powerful clue to starformation in elliptical galaxies if it proves to be general. Presentdata favor a ``frosting'' model in which low apparent SSP ages areproduced by adding a small frosting of younger stars to an older``base'' population (assuming no change in σ). If the frostingabundances are close to or slightly greater than the base population,simple two-component models run along lines of constant σ in theZ-plane, as required. This favors star formation from well-mixedpre-enriched gas rather than unmixed low-metallicity gas from anaccreted object.
| 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
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