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|The dwarf low surface brightness galaxy population of the Virgo Cluster - II. Colours and HI line observations|
In order to investigate the nature of dwarf low surface brightness (LSB)galaxies we have undertaken a deep B- and I-band CCD survey of a14-deg2 strip in the Virgo Cluster and applied a Fourierconvolution technique to explore its dwarf galaxy population down to acentral surface brightness of ~26 B magarcsec-2 and a totalabsolute B mag of ~-10. In this paper we carry out an analysis of theirmorphology, (B-I) colours and atomic hydrogen content. We compare theseproperties with those of dwarf galaxies in other environments to try andassess how the cluster environment has influenced their evolution. Fielddwarfs are generally of a more irregular morphology, are bluer andcontain relatively more gas. We assess the importance that variousphysical processes have on the evolution of cluster dwarf galaxies(ram-pressure stripping, tidal interactions, supernova-driven gas loss).We suggest that enhanced star formation triggered by tidal interactionsis the major reason for the very different general properties of clusterdwarfs: they have undergone accelerated evolution.
|Star Clusters in Virgo and Fornax Dwarf Irregular Galaxies|
We present the results of a search for clusters in dwarf irregulargalaxies in the Virgo and Fornax Clusters using Hubble Space Telescope(HST) WFPC2 snapshot data. The galaxy sample includes 28 galaxies, 11 ofwhich are confirmed members of the Virgo and Fornax Clusters. In the 11confirmed members, we detect 237 cluster candidates and determine theirV magnitudes, V-I colors, and core radii. After statistical subtractionof background galaxies and foreground stars, most of the clustercandidates have V-I colors of -0.2 and 1.4, V magnitudes lying between20 and 25 mag, and core radii between 0 and 6 pc. Using Hαobservations, we find that 26% of the blue cluster candidates are mostlikely H II regions. The rest of the cluster candidates are most likelymassive (>104 Msolar) young and old clusters. Acomparison between the red cluster candidates in our sample and theMilky Way globular clusters shows that they have similar luminositydistributions but that the red cluster candidates typically have largercore radii. Assuming that the red cluster candidates are in factglobular clusters, we derive specific frequencies (SN)ranging from ~0 to 9 for the galaxies. Although the values areuncertain, seven of the galaxies appear to have specific frequenciesgreater than 2. These values are more typical of elliptical andnucleated dwarf elliptical galaxies than they are of spiral or LocalGroup dwarf irregular galaxies.
|Radio continuum spectra of galaxies in the Virgo cluster region|
New radio continuum observations of galaxies in the Virgo cluster regionat 4.85, 8.6, and 10.55 GHz are presented. These observations arecombined with existing measurements at 1.4 and 0.325 GHz. The sampleincludes 81 galaxies where spectra with more than two frequencies couldbe derived. Galaxies that show a radio-FIR excess exhibit centralactivity (HII, LINER, AGN). The four Virgo galaxies with the highestabsolute radio excess are found within 2° of the centerof the cluster. Galaxies showing flat radio spectra also host activecenters. There is no clear trend between the spectral index and thegalaxy's distance to the cluster center.Figure 3 is only available in electronic form athttp://www.edpsciences.orgTable 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (184.108.40.206) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/1
|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
|On the local radio luminosity function of galaxies. I. The Virgo cluster|
We cross-correlate the galaxies brighter than m_B=18 in the Virgocluster with the radio sources in the NVSS survey (1.4 GHz), resultingin 180 radio-optical identifications. We determine the radio luminosityfunction of the Virgo galaxies, separately for the early- andlate-types. Late-type galaxies develop radio sources with a probabilityproportional to their optical luminosity. In fact their radio/optical(R_B) distribution is gaussian, centered at log R_B ~ -0.5, i.e. theradio luminosity is ~ 0.3 of the optical one. The probability oflate-type galaxies to develop radio sources is almost independent oftheir detailed Hubble type, except for Sa (and S0+S0a) which are afactor of ~ 5 less frequent than later types at any R_B. Giantelliptical galaxies feed ``monster" radio sources with a probabilitystrongly increasing with mass. However the frequency of fainter radiosources is progressively less sensitive on the system mass. The faintestgiant E galaxies (M_B=-17) have a probability of feeding low power radiosources similar to that of dwarf E galaxies as faint as M_B=-13. Table~1is only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|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.
|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.
|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.
|Virgo dwarfs - New light on faint galaxies|
Photographically amplified UK Schmidt plates have been used to define anew sample of low surface brightness (LSB) galaxies in the VirgoCluster. One of these galaxies is the largest, most gas-rich spiralgalaxy known, located well beyond the Virgo Cluster. The rest of the 137galaxies appear to be dwarf ellipticals. CCD photometry shows that thefaint galaxies are well modeled by an exponential radial profile. Thecolors of very LSB galaxies in Virgo are unusually blue in B-V, bluerthan the metal-poor Galactic globular clusters. If these galaxies do notviolate the mass-metallicity relation, then they must have smaller meanages than Galactic globulars. It is confirmed that any faint galaxysurvey tends to choose objects of a luminosity and surface brightnessthat give them the maximum angular size on the discovery material.
|Surface photometry of dwarf elliptical galaxies in the Virgo cluster|
Photographic surface photometry is carried out for 69 dwarf ellipticalsin the central region of the Virgo Cluster, using two plates in the Bband taken with the 2.5 m du Pont telescope at Las Campanas Observatory.Luminosity profiles and various photometric parameters are obtained, andthe following three results are derived: (1) All the dwarf ellipticalsin the sample have luminosity profiles consistent with exponential lawsexcept for six galaxies which are probably giant ellipticals in thebackground. If they are physcial members of the Virgo Cluster, they maybe identified with 'classical' dwarf ellipticals recognized by Wirth andGallagher. (2) The distribution of apparent flattenings of dwarfellipticals suggests that the population of dwarf ellipticals is notdominated by flat disk systems like spiral galaxies, in spite of theirexponential profiles. (3) Two important diagrams, a diagram ofconcentration index versus absolute magnitude and a diameter versussurface brightness diagram (DSBD), show a hint of structuraldiscontinuity in the sequence of spheroidal stellar systems consistingof giant ellilpticals, dwarf ellipticals, and globular clusters.
|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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