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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
| The faint end of the galaxy luminosity function
We present and discuss optical measurements of the faint end of thegalaxy luminosity function down to MR=-10 in five differentlocal environments of varying galaxy density and morphological content.The environments we studied, in order of decreasing galaxy density, arethe Virgo Cluster, the NGC 1407 Group, the Coma I Group, the Leo Groupand the NGC 1023 Group. Our results come from a deep wide-angle surveywith the National Astronomical Observatories of Japan Subaru 8-mTelescope on Mauna Kea and are sensitive down to very faintsurface-brightness levels. Galaxies were identified as group or clustermembers on the basis of their surface brightness and morphology. Thefaintest galaxies in our sample have R~ 22.5. There were thousands offainter galaxies but we cannot distinguish cluster members frombackground galaxies at these faint limits so do not attempt to determinea luminosity function fainter than MR=-1010. In all cases,there are far fewer dwarfs than the numbers of low-mass haloesanticipated by cold dark matter theory. The mean logarithmic slope ofthe luminosity function between MR=-1018 andMR=-1010 is α~=-1.2, far shallower than the cold darkmatter mass function slope of α~=-1.8. We would therefore need tobe missing about 90 per cent of the dwarfs at the faint end of oursample in all the environments we study to achieve consistency with CDMtheory. It is unlikely that such large numbers of dwarfs are missedbecause (i) the data are deep enough that we are sensitive to very lowsurface brightness galaxies, and (ii) the seeing is good enough that wecan have some confidence in our ability to distinguish high surfacebrightness dwarfs from background galaxies brighter than R= 22.5. Onecaveat is that we miss compact members taken to be background galaxies,but such objects (like M32) are thought to be rare.
| The luminosity function of the Virgo Cluster from MB=-22 to -11
We measure the galaxy luminosity function (LF) for the Virgo Clusterbetween blue magnitudes MB=-22 and -11 from wide-fieldcharge-coupled device (CCD) imaging data. The LF is only graduallyrising for -22
| Neutral hydrogen detection survey of dwarf galaxies. II - Faint Virgo dwarfs and a field sample
Neutral hydrogen spectra are presented for 53 faint dwarf galaxies inVirgo, completing the Arecibo survey of all late-type dwarfs in theVirgo Cluster Catalog, and for 42 dwarf galaxies from the field sampleof Binggeli et al. (1989). For detected galaxies, heliocentricvelocities, profile widths, and single-beam fluxes are tabulated. Thefield sample has been used to investigate the field luminosity functionand the clustering of dwarf galaxies vis-a-vis bright galaxies.
| Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area.
The present catalog of 2096 galaxies within an area of about 140 sq degapproximately centered on the Virgo cluster should be an essentiallycomplete listing of all certain and possible cluster members,independent of morphological type. Cluster membership is essentiallydecided by galaxy morphology; for giants and the rare class of highsurface brightness dwarfs, membership rests on velocity data. While 1277of the catalog entries are considered members of the Virgo cluster, 574are possible members and 245 appear to be background Zwicky galaxies.Major-to-minor axis ratios are given for all galaxies brighter than B(T)= 18, as well as for many fainter ones.
| A catalog of dwarf galaxies in Virgo
A catalog listing the location, apparent angular diameter, type,estimated central light concentration, and estimated brightness of 846dwarf galaxies in a 200-deg-sq region in Virgo is presented. Thegalaxies comprise 634 ellipticals, 137 IC-3475-type galaxies, 73 dwarfspirals and irregulars, and two objects which are jets of normalgalaxies, and were found on nine long-exposure IIIa-J-emulsion platesmade with the 1.2-m-Schmidt telescope at Palomar Observatory from 1971to 1976. Concordances to other catalogs, tables of additionalparameters, maps, graphs, and photographs are provided. The projecteddistributions of normal and dwarf galaxies and the dependence ofapparent luminosity on central light concentration are discussed. It isfound that dwarf ellipticals and IC-3475-type galaxies are probablemembers of the Virgo cluster, while dwarf spirals and possibly dwarfirregulars are not.
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