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|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.
|Color-Magnitude Diagrams of Resolved Stars in Virgo Cluster Dwarf Galaxies|
The Advanced Camera for Surveys (ACS) on the Hubble Space Telescope(HST) has been used to image two fields in the core of the Virgo Clusterthat contain a number of dwarf elliptical galaxies. The combined F555Wand F814W images have resolved red giant stars in these galaxies, downto 1 mag below the giant branch tip. Two of the galaxies were targetedbecause of their extremely low central surface brightnesses(Bo>27.0) thus, the successful resolution into starsconfirms the existence of such tenuous galaxies. Red giant stars werealso found that are not ostensibly associated with any galaxy.Color-magnitude diagrams in V and I have been derived for the fivedwarfs, as well as the halo of a nearby spiral galaxy and theintracluster stars in the two fields. These diagrams were used to derivedistances and metallicities via the magnitude of the red giant branchtip, and the mean color of the giant branch. The mean abundances ofstars in the dwarfs range from -1.2<[Fe/H]<-2.4, and fall alongthe relation between galaxy luminosity and metallicity found for LocalGroup and M81 group dwarf elliptical galaxies. [Fe/H] does not appear tobe well-correlated with galaxy surface brightness, as the two extremelylow surface brightness galaxies do not have extreme abundances. The meandistance modulus of the six Virgo galaxies is 31.0+/-0.05, or 16.1+/-0.4Mpc, whereas that for the intracluster stars in those fields is31.2+/-0.09 (17.4+/-0.7 Mpc).
|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.
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