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Globular cluster systems in low-luminosity early-type galaxies near the Fornax cluster centre
We present a photometric study of the globular cluster systems (GCSs) ofthe Fornax cluster galaxies NGC1374, NGC1379 and NGC1387. The dataconsist of images from the wide-field MOSAIC imager of the Cerro TololoInter-American Observatory (CTIO) 4-m telescope, obtained withWashington C and Kron-Cousins R filters. The images cover a field of 36× 36arcmin2, corresponding to 200 ×200kpc2 at the Fornax distance. Two of the galaxies, NGC1374and NGC1379, are low-luminosity ellipticals while NGC1387 is alow-luminosity lenticular. Their cluster systems are still embedded inthe cluster system of NGC1399. Therefore, the use of a large field iscrucial and some differences to previous work can be explained by this.The colour distributions of all GCSs are bimodal. NGC1387 presents aparticularly distinct separation between red and blue clusters and anoverproportionally large population of red clusters. The radialdistribution is different for blue and red clusters, red clusters beingmore concentrated towards the respective galaxies. The different colourand radial distributions point to the existence of two globular clustersubpopulations in these galaxies. Specific frequencies are in the rangeSN= 1.4-2.4, smaller than the typical values for ellipticalgalaxies. These galaxies might have suffered tidal stripping of blueglobular clusters by NGC1399.
| A wide-field photometric study of the globular cluster system of NGC 4636
Previous smaller-scale studies of the globular cluster system of NGC4636, an elliptical galaxy in the southern part of the Virgo cluster,have revealed an unusually rich globular cluster system. Were-investigate the cluster system of NGC 4636 with wide-field Washingtonphotometry. The globular cluster luminosity function can be followedroughly 1 mag beyond the turn-over magnitude found at {V} =23.31±0.13 for the blue cluster sub-population. This correspondsto a distance modulus of ({m}-{M})=31.24±0.17, 0.4 mag largerthan the distance determined from surface brightness fluctuations. Thehigh specific frequency is confirmed, yet the exact value remainsuncertain because of the uncertain distance: it varies between5.6±1.2 and 8.9±1.2. The globular cluster system has aclearly bimodal color distribution. The color peak positions show noradial dependence and are in good agreement with the values found forother galaxies studied in the same filter system. However, a luminositydependence is found: brighter clusters with an“intermediate” color exist. The clusters exhibit a shallowradial distribution within 7´, represented by a power-law with anexponent of -1.4. Within the same radial interval, the galaxy light hasa distinctly steeper profile. Because of the difference in the clusterand light distribution the specific frequency increases considerablywith radius. At 7´ and 9´ the density profiles of the redand blue clusters, respectively, change strongly: the power-law indicesdecrease to around -5 and become similar to the galaxy profile. Thissteep profile indicates that we reach the outer rim of the clustersystem at approximately 11´. This interpretation is supported bythe fact that in particular the density distribution of the blue clusterpopulation can be well fit by the projection of a truncated power-lawmodel with a core. This feature is seen for the first time in a globularcluster system. While the radial distribution of the cluster and fieldpopulations are rather different, this is not true for the ellipticityof the system: the elongation as well as the position angle of thecluster system agree well with the galaxy light. We compare the radialdistribution of globular clusters with the light profiles for a sampleof elliptical galaxies. The difference observed in NGC 4636 is typicalof an elliptical galaxy of this luminosity. The intrinsic specificfrequency of the blue population is considerably larger than that of thered one.Tables A.1 to A.6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/433/43
| 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.
| Companions to Isolated Elliptical Galaxies: Revisiting the Bothun-Sullivan Sample
We investigate the number of physical companion galaxies for a sample ofrelatively isolated elliptical galaxies. The NASA/IPAC ExtragalacticDatabase (NED) has been used to reinvestigate the incidence of satellitegalaxies for a sample of 34 elliptical galaxies, first investigated byBothun & Sullivan using a visual inspection of Palomar Sky Surveyprints out to a projected search radius of 75 kpc. We have repeatedtheir original investigation using data cataloged in NED. Nine of theseelliptical galaxies appear to be members of galaxy clusters; theremaining sample of 25 galaxies reveals an average of +1.0+/-0.5apparent companions per galaxy within a projected search radius of 75kpc, in excess of two equal-area comparison regions displaced by 150-300kpc. This is significantly larger than the +0.12+/-0.42companions/galaxy found by Bothun & Sullivan for the identicalsample. Making use of published radial velocities, mostly availablesince the completion of the Bothun-Sullivan study, identifies thephysical companions and gives a somewhat lower estimate of +0.4companions per elliptical galaxy. This is still 3 times larger than theoriginal statistical study, but given the incomplete and heterogeneousnature of the survey redshifts in NED, it still yields a firm lowerlimit on the number (and identity) of physical companions. An expansionof the search radius out to 300 kpc, again restricted to sampling onlythose objects with known redshifts in NED, gives another lower limit of4.5 physical companions per galaxy. (Excluding five elliptical galaxiesin the Fornax Cluster, this average drops to 3.5 companions perelliptical.) These physical companions are individually identified andlisted, and the ensemble-averaged radial density distribution of theseassociated galaxies is presented. For the ensemble, the radial densitydistribution is found to have a falloff consistent withρ~R-0.5 out to approximately 150 kpc. For non-FornaxCluster companions the falloff continues out to the 300 kpc limit of thesurvey. The velocity dispersion of these companions is found to reach amaximum of 350 km s-1 at around 120 kpc, after which theyfall at a rate consistent with Keplerian falloff. This falloff may thenindicate the detection of a cut-off in the mass-density distribution inthe elliptical galaxies' dark matter halo at ~100 kpc.
| The surface brightness and colour-magnitude relations for Fornax cluster galaxies
We present BVI photometry of 190 galaxies in the central 4 ×3deg2 region of the Fornax cluster observed with the MichiganCurtis Schmidt Telescope. Results from the Fornax Cluster SpectroscopicSurvey (FCSS) and the Flair-II Fornax Surveys have been used to confirmthe membership status of galaxies in the Fornax Cluster Catalogue (FCC).In our catalogue of 213 member galaxies, 92 (43 per cent) have confirmedradial velocities.In this paper, we investigate the surface brightness-magnitude relationfor Fornax cluster galaxies. Particular attention is given to the sampleof cluster dwarfs and the newly discovered ultracompact dwarf galaxies(UCDs) from the FCSS. We examine the reliability of the surfacebrightness-magnitude relation as a method for determining clustermembership and find that at surface brightnesses fainter than 22 magarcsec-2, it fails in its ability to distinguish betweencluster members and barely resolved background galaxies. Cluster membersexhibit a strong surface brightness-magnitude relation. Both elliptical(E) galaxies and dwarf elliptical (dE) galaxies increase in surfacebrightness as luminosity decreases. The UCDs lie off the locus of therelation.B-V and V-I colours are determined for a sample of 113 cluster galaxiesand the colour-magnitude relation is explored for each morphologicaltype. The UCDs lie off the locus of the colour-magnitude relation. Theirmean V-I colours (~1.09) are similar to those of globular clustersassociated with NGC 1399. The location of the UCDs on both surfacebrightness and colour-magnitude plots supports the `galaxy threshing'model for infalling nucleated dwarf elliptical (dE, N) galaxies.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| The M/L vs M Relation and the Tilt of the Fundamental Plane
With extended kinematical data, we explore the tilt of the Fundamental Plane - commonly interpreted as a relation between mass and mass-to-light ratio for the elliptical galaxies. We show that dynamical non-homology is largely responsible for the tilt of the Fundamental Plane, and that when the non-homology is accounted for, no correlation is found between mass and mass-to-light ratio.
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| Extended stellar kinematics of elliptical galaxies in the Fornax cluster
We present extended stellar kinematics for a sample of ellipticalgalaxies in the Fornax cluster. Out of the 13 galaxies presented here,five (FCC 119, FCC 136, NGC 1373, NGC 1428, FCC 335) have no previouslypublished kinematical data. Major-axis velocity dispersion profiles(VDPs) and rotation curves (RCs) are given for 12 of the galaxies. Amajor feature of this data is the spatial extension: for 8 galaxies thedata extends beyond 1 R_e, and for 5 it extends beyond 2 R_e. Comparedto the previously available data, this corresponds to an increase inspatial coverage by a factor from 1 to 5. The present sample represents86% of the ellipticals in Fornax brighter than B_T = 15 mag. Five of theellipticals in the sample turn out to be rotationally-supported systems,having positive rotation parameter log ((V)/(sigma ))(*) . One of thesefive, and another 3 galaxies from the remaining sample, display evidencefor bar-like kinematics. The data indicate that the true number of``dynamically hot'' stellar systems, is much lower than previouslythought: of the Es in the present sample only 1/4 are confirmed as``pressure-supported'' systems. The data reveal a host of individualpeculiarities, like: wiggles, strong gradients, and asymmetries in therotation curve and/or in the velocity dispersion profile, thus showingthat the presence of kinematically distinct components and/ortriaxiality is a common characteristic of this class of object. Based onobservations collected at Siding Spring Observatory. Table 3 ispresented in electronic form only, and is available from the CDS,Strasbourg via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| A catalogue of Mg_2 indices of galaxies and globular clusters
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 130.79.128.5. Table 2 is available both in text and electronic form.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| Extragalactic Globular Clusters. IV. The Data
We have explored the use of absorption line strength indices, measuredfrom integrated globular cluster spectra, to predict mean metallicity inlate-type stellar systems. In previous papers we identified the bestindices for such metallicity calibrations out of ~13 measured in a largesample of galactic and M31 cluster spectra. In this paper we present theindividual measurements of 13 indices and averages of multiplemeasurements, where appropriate. Data are given for 151 M31 globularclusters, 88 galaxies, 22 M33 cluster candidates, 10 M87 clusters, eightM81 globular clusters, three Fornax dwarf galaxy clusters, "standard"stars from the lists of Faber et al., stars in the open cluster NGC 188and, for completeness, other stars observed as candidate globularclusters.
| A New I-Band Tully-Fisher Relation for the Fornax Cluster: Implication for the Fornax Distance and Local Supercluster Velocity Field
The Fornax Cluster represents an important step in the extragalacticdistance scale. Here we present a new I-band luminosity-H I velocitywidth (I-band Tully-Fisher) study of the cluster using an enlargedsampled of spiral galaxies in Fornax. I-band CCD photometry and 21 cmparameters are measured for 23 members of Fornax and compared with datafor the Virgo Cluster. We obtain an accurate distance modulus of Fornaxrelative to Virgo of -0.06 +/- 0.15 mag. The low scatter of Fornaxgalaxies around the Tully-Fisher relation will make the cluster an idealcalibrator once a direct measurement of its distance is obtained.Furthermore, the H I content of the galaxies does not seem affected bythe cluster environment. Here we use two different absolute calibrationmethods which yield an absolute distance to Fornax of 15.4 +/- 2.3 Mpc(absolute distance modulus of 30.94 +/- 0.33 mag). A simple model yieldsa Local Group Virgocentric flow velocity of 224 +/- 90 km s^-1^ whichcorresponds to a Hubble constant of H_0_ = 74 +/- 11 km s^-1^ Mpc^-1^from the Fornax data.
| Interstellar MG II Absorption Lines from Low-Redshift Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...448..634B&db_key=AST
| On the Shape of the Light Profiles of Early Type Galaxies - Part Two - the - Diagram
We present new evidence against the universality of the de Vaucouleursr^1/4^ law, considered to be the best empirical formula for fitting thelight profiles of elliptical galaxies, through the analysis of theproperties of the (D_n_/A_e_)-<μ>_e_ diagram for avolume-limited sample of early-type galaxies that are members of theVirgo and Fornax clusters. The r^1/4^ law turns out to be only aparticular case of the more general r^1/4^ law, where the exponent m isfound to correlate with the effective radius of the galaxy. We compareour sample of early-type galaxies with that studied by Burstein et al.,and find that the observed differences can be explained in terms ofprocedures and methodologies adopted for measuring the globalphotometric parameters such as total luminosities, effective radii,effective surface brightnesses and D_n_ diameters.
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