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Virgo Cluster Early-Type Dwarf Galaxies with the Sloan Digital Sky Survey. I. On the Possible Disk Nature of Bright Early-Type Dwarfs
We present a systematic search for disk features in 476 Virgo Clusterearly-type dwarf (dE) galaxies. This is the first such study of analmost-complete, statistically significant dE sample, which includes allcertain or possible cluster members with mB<=18 that arecovered by the optical imaging data of the Sloan Digital Sky Survey DataRelease 4. Disk features (spiral arms, edge-on disks, or bars) wereidentified by applying unsharp masks to a combined image from threebands (g, r, and i), as well as by subtracting the axisymmetric lightdistribution of each galaxy from that image. Fourteen objects areunambiguous identifications of disks, 10 objects show ``probable disk''features, and 17 objects show ``possible disk'' features. The numberfraction of these galaxies, for which we introduce the term ``dEdi,''reaches more than 50% at the bright end of the dE population anddecreases to less than 5% for magnitudes mB>16. Althoughpart of this observed decline might be due to the lower signal-to-noiseratio at fainter magnitudes, we show that it cannot be caused solely bythe limitations of our detection method. The luminosity function of ourfull dE sample can be explained by a superposition of dEdis and ordinarydEs, strongly suggesting that dEdis are a distinct type of galaxy. Thisis supported by the projected spatial distribution: dEdis show basicallyno clustering and roughly follow the spatial distribution of spirals andirregulars, whereas ordinary dEs are distributed similarly to thestrongly clustered E/S0 galaxies. While the flattening distribution ofordinary dEs is typical for spheroidal objects, the distribution ofdEdis is significantly different and agrees with their being flat oblateobjects. We therefore conclude that the dEdis are not spheroidalgalaxies that just have an embedded disk component but are instead apopulation of genuine disk galaxies. Several dEdis display well-definedspiral arms with grand-design features that clearly differ from theflocculent, open arms typical for late-type spirals that have frequentlybeen proposed as progenitors of dEs. This raises the question of whatprocess is able to create such spiral arms-with pitch angles like thoseof Sab/Sb galaxies-in bulgeless dwarf galaxies.
| Diffuse Light in the Virgo Cluster
We present deep optical imaging of the inner ~1.5d×1.5d of theVirgo Cluster to search for diffuse intracluster light (ICL). Our imagereaches a 1 σ depth of μV=28.5 magarcsec-2, which is 1.5 mag arcsec-2 deeper thanprevious surveys, and reveals an intricate web of diffuse ICL. We seeseveral long (>100 kpc) tidal streamers, as well as a myriad ofsmaller scale tidal tails and bridges between galaxies. The diffuse haloof M87 is traced out to nearly 200 kpc, appearing very irregular onthese scales, while significant diffuse light is also detected aroundthe M84/M86 pair. Several galaxies in the core are embedded in commonenvelopes, suggesting they are true physical subgroups. The complexsubstructure of Virgo's diffuse ICL reflects the hierarchical nature ofcluster assembly, rather than being the product of smooth accretionaround a central galaxy.
| The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei, and Stellar Halos
We present the results of a Hubble Space Telescope WFPC2 F555W and F814Wsurvey of 69 dwarf elliptical galaxies (dEs) in the Virgo and FornaxClusters and Leo Group. The V-I colors of the dE globular clusters,nuclei, and underlying field-star populations are used to trace the dEstar formation histories. We find that the dE globular clustercandidates are as blue as the metal-poor globular clusters of the MilkyWay. The observed correlation of the dE globular cluster systems' V-Icolor with the luminosity of the host dE is strong evidence that theglobular clusters were formed within the halos of dEs and do not have apregalactic origin. Assuming that the majority of dE clusters are old,the mean globular cluster color-host galaxy luminosity correlationimplies a cluster metallicity-galaxy luminosity relation of~L0.22+/-0.05B, which issignificantly shallower than the field-star metallicity-host galaxyluminosity relationship observed in Local Group dwarfs(~L0.4). The dE stellar envelopes are0.1-0.2 mag redder in V-I than their globular clusters and nuclei. Thiscolor offset implies separate star formation episodes within the dEs forthe clusters and field stars, while the very blue colors of two dEnuclei trace a third star formation event in those dEs less than 1 Gyrago.
| Distances, Metallicities, and Ages of Dwarf Elliptical Galaxies in the Virgo Cluster from Surface Brightness Fluctuations
We have employed FORS1 and 2 at the Very Large Telescope at the EuropeanSouthern Observatory (ESO) to acquire deep B and R-band CCD images of 16dwarf elliptical (dE) galaxies in the direction of the Virgo cluster.For each dwarf, we measure the apparent R-band surface brightnessfluctuation (SBF) magnitude mR and the (B-R)0color in a number of fields at different galactocentric distances. Fromthe field-to-field variation of the two quantities, we determine the SBFdistance by means of the (B-R)0-MR relation. Thederived distances of the dwarfs range from 14.9 to 21.3 Mpc, with a mean1 σ uncertainty of 1.4 Mpc or 8% of the distance, which confirmsthat there is considerable depth in the distance distribution ofearly-type cluster members. For VCC 1104 (IC 3388), our SBF distancemodulus of (m-M)SBF=31.15+/-0.19 (17.0+/-1.5 Mpc) is in goodagreement with the Harris et al result of(m-M)TRGB=30.98+/-0.19 mag (15.7+/-1.5 Mpc) based on HubbleSpace Telescope (HST) observations and the tip magnitude of the redgiant branch. Combining our results with existing distances for giantVirgo ellipticals, we identify two major galaxy concentrations in thedistance distribution: a broad primary clump around (M-m)=31.0 mag (15.8Mpc) and a narrow secondary clump around 31.33 mag (18.5 Mpc). Anadaptive kernel analysis finds the two concentrations to be significantat the 99% (2.5 σ) and 89% (1.6 σ) levels, respectively.While the near-side clump of Virgo early-type galaxies can be associatedwith the subcluster centered on M87, the second clump is believed to bemainly due to the far side infalling group of galaxies around M86. Theages and metallicities of the dE stellar populations are estimated bycombining the observed (B-R)0 colors with Worthey's stellarpopulation synthesis models. It appears that the Virgo dE galaxies covera wider range in metallicity, from [Fe/H]~-1.4 (VCC 0815) to -0.5 (NGC4415), than Fornax cluster dEs. The derived metallicities place theVirgo dEs on the extension of the metallicity-luminosity relationdefined by the low-luminosity Local Group dEs. The data further suggestan age range from genuinely old (~17 Gyr) stellar systems such as IC3019 and IC 0783 to intermediate-age (8-12 Gyr) dwarfs such as NGC 4431and IC 3468.
| The origin of H I-deficiency in galaxies on the outskirts of the Virgo cluster. II. Companions and uncertainties in distances and deficiencies
The origin of the deficiency in neutral hydrogen of 13 spiral galaxieslying in the outskirts of the Virgo cluster is reassessed. If thesegalaxies have passed through the core of the cluster, their interstellargas should have been lost through ram pressure stripping by the hotX-ray emitting gas of the cluster. We analyze the positions of these HI-deficient and other spiral galaxies in velocity-distance plots, inwhich we include our compilation of velocity-distance data on 61elliptical galaxies, and compare with simulated velocity-distancediagrams obtained from cosmological N-body simulations. We find that20% relative Tully-Fisher distance errors are consistent with thegreat majority of the spirals, except for a small number of objectswhose positions in the velocity-distance diagram suggest grosslyincorrect distances, implying that the Tully-Fisher error distributionfunction has non-Gaussian wings. Moreover, we find that the distanceerrors may lead to an incorrect fitting of the Tolman-Bondi solutionthat can generate significant errors in the distance and especially themass estimates of the cluster. We suggest 4 possibilities for theoutlying H I-deficient spirals (in decreasing frequency): 1) they havelarge relative distance errors and are in fact close enough (atdistances between 12.7 and 20.9 Mpc from us) to the cluster to havepassed through its core and seen their gas removed by ram pressurestripping; 2) their gas is converted to stars by tidal interactions withother galaxies; 3) their gas is heated during recent mergers withsmaller galaxies; and 4) they are not truly H I-deficient (e.g. S0/amisclassified as Sa).Appendix A is only available in electronic form athttp://www.edpsciences.org
| Galaxy Formation and the GTC
A review of faint galaxy counts and redshift surveys points to ascientific opportunity for the Gran Telecopio Canarias (GTC) to answer abasic question about galaxy formation: How and when did mass assemble?We argue that the key to answering this question is by focusing on the``faint-end'' of the galaxy luminosity function out to at least z = 2.This can be exploited with a concerted effort starting with deep countsin the optical and near infrared, followed with near-infraredmultiobject spectroscopy, and completed with integral field spectroscopyemploying adaptive optics.
| Galaxy Populations and Evolution in Clusters. IV. Deep H I Observations of Dwarf Elliptical Galaxies in the Virgo Cluster
In this paper we present deep Arecibo H I and WIYN optical observationsof Virgo Cluster dwarf elliptical galaxies. Based on this data we arguethat a significant fraction of low-mass galaxies in the Virgo Clusterrecently underwent evolution. Our new observations consist of H I 21 cmline observations for 22 classified dE galaxies with optical radialvelocities consistent with membership in the Virgo Cluster. Clustermembers VCC 390 and VCC 1713 are detected with H I massesMHI=6×107 and 8×107Msolar, respectively, while MHI values in theremaining 20 dE galaxies have upper limits as low as~5×105 Msolar. We combine our results withthose for 26 other Virgo Cluster dE galaxies with H I observations inthe literature, seven of which have H I detection claims. New opticalimages from the WIYN telescope of five of these H I-detected dEgalaxies, along with archival data, suggest that seven of the claimeddetections are true H I detections, yielding a ~15% detection rate.These H I-detected, classified dE galaxies are preferentially locatednear the periphery of the Virgo Cluster. Three Virgo dE galaxies haveobserved H I velocity widths greater than 200 km s-1,possibly indicating the presence of a large dark matter content ortransient extended H I. We discuss the possible origins of these objectsand argue that they originate from field galaxies accreted onto highangular momentum orbits by Virgo in the last few Gyr. As a result ofthis, we argue, these galaxies are slowly transformed within the clusterby gradual gas-stripping processes, associated truncation of starformation, and passive fading of stellar populations. Low-mass,early-type cluster galaxies are therefore currently being produced asthe product of cluster environmental effects. We utilize our results ina simple model to estimate the recent (past 1-3 Gyr) average massaccretion rate into the Virgo Cluster, deriving a value of M~50Msolar yr-1.
| Internal Dynamics, Structure, and Formation of Dwarf Elliptical Galaxies. II. Rotating versus Nonrotating Dwarfs
We present spatially resolved internal kinematics and stellar chemicalabundances for a sample of dwarf elliptical (dE) galaxies in the VirgoCluster observed with the Keck telescope and Echelle Spectrograph andImager. In combination with previous measurements, we find that four outof 17 dE's have major-axis rotation velocities consistent withrotational flattening, while the remaining dE's have no detectablemajor-axis rotation. Despite this difference in internal kinematics,rotating and nonrotating dE's are remarkably similar in terms of theirposition in the fundamental plane, morphological details, stellarpopulations, and local environment. We present evidence for (or confirmthe presence of) faint underlying disks and/or weak substructure in afraction of both rotating and nonrotating dE's, but a comparable numberof counterexamples exist for both types that show no evidence of suchstructure. Absorption line strengths were determined based on theLick/IDS system (Hβ, Mg b, Fe5270, and Fe5335) for the centralregion of each galaxy. We find no difference in the line-strengthindices, and hence stellar populations, between rotating and nonrotatingdE galaxies. The best-fitting mean age and metallicity for our same of17 dE's are 5 Gyr and [Fe/H]=-0.3 dex, respectively, with rms spreads of3 Gyr and 0.1 dex. The majority of dE's are consistent with solar[α/Fe] abundance ratios. By contrast, the stellar populations ofclassical elliptical galaxies are, on average, older, more metal-rich,and α-enhanced relative to our dE sample. The line strengths ofour dE's are consistent with the extrapolation of the line strengthversus velocity dispersion trend seen in classical elliptical galaxies.Finally, the local environments of both rotating and nonrotating dE'sappear to be diverse in terms of their proximity to larger galaxies inreal or velocity space within the Virgo Cluster. Thus, rotating andnonrotating dE's are remarkably similar in terms of their structure,stellar content, and local environments, presenting a significantchallenge to theoretical models of their formation.Data presented herein were obtained at the W. M. Keck Observatory, whichis operated as a scientific partnership among the California Instituteof Technology, the University of California, and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W. M. Keck Foundation.
| Companions of Bright Barred Shapley-Ames Galaxies
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.
| VLT surface photometry and isophotal analysis of early-type dwarf galaxies in the Virgo cluster
We have carried out surface photometry and an isophotal analysis for asample of 25 early-type dwarf (dE and dS0) galaxies in the Virgo clusterbased on CCD images taken at the VLT with FORS1 and FORS2. For eachgalaxy we present B and R-band surface brightness profiles, as well asthe radial colour (B-R) profile. We give total apparent BR magnitudes,effective radii, effective surface brightnesses and total colourindices. The light profiles have been fitted with Sérsic modelsand the corresponding parameters are compared to the ones for otherclasses of objects. In general, dEs and dS0s bridge the gap in parameterspace between the giant ellipticals and the low-luminosity dwarfspheroidals in the Local Group, in accordance with previous findings.However, the observed profiles of the brightest cluster dwarfs showsignificant deviations from a simple Sérsic model, indicatingthat there is more inner structure than just a nucleus. This picture isreinforced by our isophotal analysis where complex radial dependenciesof ellipticity, position angle, and isophotal shape parameter a_4 areexhibited not only by objects like IC 3328, for which the presence of adisk component has been confirmed, but by many apparently normal dEs aswell. In addition, we find a relation between the effective surfacebrightness, at a given luminosity, and the strength of the offset of thegalaxy's nucleus with respect to the center of the isophotes. Dwarfswith large nuclear offsets also tend to have stronger isophotal twists.However, such twists are preferentially found in apparently round(epsilon < 0.3) galaxies and are always accompanied by significantradial changes of the ellipticity, which clearly points to a projectioneffect. In sum, our findings suggest the presence of substructure inmost, and preferentially in the less compact, bright early-type dwarfs.The physical (dynamical) meaning of this has yet to be explored.Based on observations collected at the European Southern Observatory(ESO 63.O-0055 and 65.N-0062).Figure \ref{fig1} is only available in electronic form athttp://www.edpsciences.org
| A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
| Embedded disks in Fornax dwarf elliptical galaxies
We present photometric and kinematic evidence for the presence ofstellar disks, seen practically edge-on, in two Fornax dwarf galaxies,FCC 204 (dS0(6)) and FCC 288 (dS0(7)). This is the first time suchstructures have been identified in Fornax dwarfs. FCC 288 has only asmall bulge and a bright flaring and slightly warped disk that can betraced out to +/- 23 arcsec from the center (2.05 kpc for H_0=75 kms-1 Mpc-1). FCC 204's disk can be traced out to+/-20 arcsec (1.78 kpc). This galaxy possesses a large bulge. Theseresults can be compared to the findings of Jerjen et al. (\cite{jer00})and Barazza et al. (\cite{bar02}) who discovered nucleated dEs withspiral and bar features in the Virgo Cluster.Based on observations collected at the European Southern Observatory,Chile (ESO Large Programme Nr. 165.N-0115).
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| More evidence for hidden spiral and bar features in bright early-type dwarf galaxies
Following the discovery of spiral structure in IC 3328 (Jerjen et al.\cite{Jerjen2000}), we present further evidence that a sizable fractionof bright early-type dwarfs in the Virgo cluster are genuine diskgalaxies, or are hosting a disk component. Among a sample of 23nucleated dwarf ellipticals and dS0s observed with the Very LargeTelescope in B and R, we found another four systems exhibitingnon-axisymmetric structures, such as a bar and/or spiral arms,indicative of a disk (IC 0783, IC 3349, NGC 4431, IC 3468). Particularlyremarkable are the two-armed spiral pattern in IC 0783 and the bar andtrailing arms in NGC 4431. For both galaxies the disk nature hasrecently been confirmed by a rotation velocity measurement (Simien &Prugniel \cite{Simien2002}). Our photometric search is based on aFourier decomposition method and a specific version of unsharp masking.Some ``early-type'' dwarfs in the Virgo cluster seem to be formerlate-type galaxies which were transformed to early-type morphology, e.g.by ``harassment'', during their infall to the cluster, while maintainingpart of their disk structure. Based on observations collected at theEuropean Southern Observatory, Chile.
| Galaxy Populations and Evolution in Clusters. I. Dynamics and the Origin of Low-Mass Galaxies in the Virgo Cluster
Early-type dwarfs are the most common galaxy in the local universe, yettheir origin and evolution remain a mystery. Various cosmologicalscenarios predict that dwarf-like galaxies in dense areas are the firstto form and hence should be the oldest stellar systems in clusters. Byusing radial velocities of early-type dwarfs in the Virgo cluster wedemonstrate that these galaxies are not an old cluster population buthave signatures of production from the infall of field galaxies.Evidence of this includes the combined large dispersions andsubstructure in spatial and kinematic distributions for Virgo early-typedwarfs and a velocity dispersion ratio with giant ellipticals expectedfor virialized and accreted populations. We also argue that thesegalaxies cannot originate from accreted field dwarfs, but must havephysically evolved from a precursor population, of different morphology,that fell into Virgo some time in the past.
| Off-center nuclei in dwarf elliptical galaxies
We have searched for off-center nuclei in 78 ``nucleated'' dwarfelliptical (dE,N) galaxies, drawing on digitized photographic imagesfrom a previous study of Virgo cluster dwarfs. The search is based on asimple algorithm which compares the center coordinates of a series ofouter elliptical isophotes with the position of the galaxy's nucleus.Monte Carlo simulations of the measuring procedure are used to assessrandom and systematic errors. Roughly 20% of all dwarf nuclei in thesample (neglecting uncertain cases) are found to be significantlyoff-centered. The typical displacement is 1arcsec , or 100 pc (assuminga Virgo cluster distance of 20 Mpc), corresponding to 0.5 to 1 effectiveradii of the dwarf galaxy. There is a tendency of the nuclear off-centerdisplacement to increase with decreasing surface brightness of theunderlying galaxy. A similar trend was found with normal ellipticalgalaxies before. If real, the effect could mean that a nucleus canoscillate about the galaxy center with larger amplitude in a shallower(less cuspy) gravitational potential. In an appendix we present evidencefor the existence of a strong, unambiguous relation between the nuclearmagnitude and the ellipticity of dE,N galaxies. If a nucleus iscomprising 4% or more of the total light of the underlying galaxy, thatgalaxy is nearly always round, i.e. ellipticity less than 0.15 (dE0,dE1). This effect was predicted qualitatively long ago as the result ofbox orbit disruption caused by a central massive compact object (blackhole).
| One Arc Degree Core Substructure of the Virgo Cluster
Not Available
| 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.
| The ``Virgo photometry catalogue''; a catalogue of 1180 galaxies in the direction of the Virgo Cluster's core
We present a new catalogue of galaxies in the direction of the VirgoCluster's core: the Virgo Photometry Catalogue (VPC)*. This cataloguecontains 1180 galaxies (including background objects) within a 23square-degree area of the sky centred on R.A._{1950.0} = 12h 26m anddec._{1950.0} = 13(deg) 08'. The VPC galaxy sample comprises ofnon-stellar objects brighter than B_J25 = 19.0; thecompleteness limits being B_J25 ~18.5 for the northern halfof the survey area and B_J25 ~18.0 for the southern half.Independently-calibrated photographic surface photometry is presentedfor over 1000 galaxies in the U, B_J and R_C bands. Parameters listedfor catalogued galaxies include: equatorial coordinates, morphologicaltypes, surface-brightness profile parameters (which preserve themajority of the original surface photometry information), U, B_J &R_C isophotal magnitudes, B_J and [transformed] B total magnitudes,(U-B_J) and (B_J-R_C) equal-area and total colours, apparent angularradii, ellipticities, position angles, heliocentric radial velocitiesand alternative designations. All total magnitudes and total colours areextrapolated according to a new system denoted t in order to distinguishit from the T system already in use. The VPC is based primarily on four(one U, two B_J and one R_C) UK-Schmidt plates, all of which weredigitised using the Royal Observatory Edinburgh's (ROE) COSMOS measuringmachine. All magnitudes, colours and surface-brightness parameters arederived from numerical integrations of segmented plate-scan data, exceptfor (in 109 cases) saturated or (in 51 cases) inextricably-mergedimages; our segmentation software being able to cope with the vastmajority of image mergers. * Appendices B, C and E, which contain thesurface photometry, the main catalogue and the summary cataloguerespectively, are only available in electronic form. They can beobtained from La Centre des Donees astronomiques de Strasbourg (CDS) viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html.
| Is the shape of the luminosity profile of dwarf elliptical galaxies an useful distance indicator?
The shape of the surface brightness profile of dE galaxies, quantifiedby parameter n of Sersic's generalized profile law, has recently beenput forward as new extragalactic distance indicator (Young & Currie1994). Its application to the Virgo cluster has subsequently led to theclaim that the Virgo dEs are not lying in the cluster core but aredistributed in a prolate structure stretching from 8 to 20 Mpc distance(Young & Currie 1995). This claim is refuted here. We have fitted aSersic law to the surface brightness profiles of 128 Virgo cluster dEsand dS0s from the photometry of Binggeli & Cameron (1991). Thedispersion of the n - M relation is indeed large (sigma_rms ~ 0.9 mag).However, we argue that this scatter is not due to the depth of the Virgocluster, but is essentially intrinsic. Contrary to what one would expectfrom the cluster depth hypothesis, there is no clearvelocity-``distance'' relation for a sample of 43 Virgo dEs and dS0swith known redshifts. The analysis of Young & Currie (1995) ishampered by the use of low-resolution photometry and flawed by theassumption that the n - M and n - R relations can be used independently.By combining different Sersic law parameters, the scatter of the scalingrelations can be reduced somewhat, but never below sigma_rms ~ 0.7 mag,at least for the Virgo cluster. For the purpose of distancemeasurements, this falls short of the well-established Tully-Fisher andD_n - sigma methods, and it is comparable to what one can get alreadyfrom the < mu >_eff - M relation for dEs, which does not requireany profile modelling.
| 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.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| Distances to 64 Virgo dwarf-elliptical galaxies and the depth in their spatial distribution
We derive distances for 64 dwarf ellipticals (dEs) in the direction ofthe Virgo cluster's (VC) core, by means of the luminosity-profilecurvature (L-n) relationship and by means of their global scalelengths,which we find to be correlated with the shapes of theirsurface-brightness profiles. The great depth we find in the spatialdistribution of Virgo dEs is not consistent with a unimodal distributiondue to a single spherically symmetric concentration of galaxies. Thisdepth is also sufficient to explain much of the disagreement over theVC's distance, and thereby much of the Hubble-constant (H_0)controversy.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| Dwarf galaxies in the Virgo cluster. II - Photometric techniques and basic data
Results are presented of photographic surface photometry carried out for305 (mostly dwarf) galaxies in the Virgo cluster, in which the galaxyimages were digitized on 14 of the 67 du Pont plates used for the Virgocluster survey. Azimuthally averaged surface brightness profiles areshown for all galaxies. The following model-free photometric parametersare derived and listed for each galaxy: total apparent blue magnitude,mean effective radius and surface brightness, and various isophotalradii, ellipticity, and position angle. Most galaxies were fitted by anexponential form and/or a King model profile. The best-fittingparameters, including the 'nuclear' (central residual) magnitudes fordE+dS0 galaxies, are listed.
| Extragalactic globular clusters. III - Metallicity comparisons and anomalies
A method based on the strengths of six absorption line indices measuredin integrated spectra is used to derive metallicities for 22 globularclusters associated with the Sc galaxy, M33, 10 globular clusters withthe giant elliptical galaxy, M87, eight globular clusters associatedwith the Sb(r)I-II galaxy, M81, and three globular clusters associatedwith the Fornax dwarf elliptical galaxy. Mean metallicities are derivedfor 38 bright galaxies, mostly ellipticals, 29 dwarf elliptical galaxiesin the Virgo cluster, 10 dwarf elliptical galaxies in the Fornaxcluster, and four local group dwarf galaxies. These results are comparedwith previously derived metallicities for 149 clusters in M31 and withthe Milky Way cluster metallicities to show that the mean metallicity ofa cluster system is linearly related to the luminosity of the parentgalaxy. A similar relationship is suggested between galaxy metallicityand luminosity for the bright and dwarf galaxies.
| Dwarf galaxies in the Virgo cluster. I - The systematic photometric properties of early-type dwarfs
The azimuthally averaged surface brightness profiles of 200 faintearly-type Virgo cluster galaxies have been analyzed. Faint dwarfs arevery well described by an exponential or a King model. The magnitudes ofthe nuclei vary greatly at a given galaxian magnitude, but the maximumnuclear luminosity is a strong function of M(T). In the 0.1-1 kpc radiusrange, the logarithmically plotted profiles of all early-type galaxiescome in two well-defined classes identified with classical types versusdwarf types. The former are all classified E or S0, while the lattercomprise all galaxies classified dE or dS0, all morphologically'intermediate' types, and even two classified 'E'. The mean SB profilesof dS0 galaxies are indistinguishable from bright dE profiles. In 2D,the dS0s appear highly flattened and/or show asymmetric and irregularfeatures which may indicate their disk nature.
| The surface brightness test for the expansion of the universe. II - Radii, surface brightness, and absolute magnitude correlations for nearby E galaxies
Data for elliptical galaxies in the Virgo, Fornax, and Coma clusters andin the general field are analyzed in order to determine the dispersionin average surface brightness. The data are discussed using measures ofboth the effective radius and the Petrosian r(eta) radii. The dispersionis found to be about 0.5 mag after reducing the data to absolutemagnitude M(B) = -22. This value is smaller than the 1.8 mag Tolman (1 +z) exp 4 factor, even at the modest redshift of z = 0.5, showing thatthe Tolman test is feasible in practice as well as in principle.
| The use of dwarf elliptical galaxies as distance indicators - The relative distances between Virgo, Fornax, and Centaurus
Photometric parameters derived from surface photometry of dwarfelliptical galaxies are used to determine the relative distance betweenthe Virgo, Fornax, and Centaurus clusters. The study uses a sample ofabout 25 dwarf elliptical galaxies in each cluster. With Virgo as thefiducial cluster, it is found that R(Fornax)/R(Virgo) = 0.93 + or - 0.07and R(Centaurus)/R(Virgo) = 1.91 + or - 0.07. The results are in goodagreement with those obtained by Aaronson et al. (1989) using the IRTully-Fisher relation.
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