Jeff Secker

Dwarf Galaxies in the Coma Cluster. II. Photometry and Analysis

We use the data set derived in our previous paper (Secker & Harris 1997) to study the dwarf galaxy population in the central 700 arcmin2 of the Coma cluster, the majority of which are early-type dwarf elliptical (dE) galaxies. Analysis of the statistically-decontaminated dE galaxy sequence in the color-magnitude diagram reveals that the mean dE color at R = 18.0 mag is (B-R) 1.4 mag, but that a highly significant trend of color with magnitude exists (Delta (B-R)/Delta R = -0.056±0.002 mag) in the sense that fainter dEs are bluer and thus presumably more metal-poor. The mean color of the faintest dEs in our sample is (B-R) 1.15 mag, consistent with a color measurement of the diffuse intracluster light in the Coma core. This intracluster light could then have originated from the tidal disruption of faint dEs in the cluster core. The total galaxy luminosity function (LF) is well modeled as the sum of a log-normal distribution for the giant galaxies, and a Schechter function for the dE galaxies with a faint-end slope alpha = -1.41±0.05. This value of alpha is consistent with those measured for the Virgo and Fornax clusters. The spatial distribution of the faint dE galaxies (19.0 < R ≤ 22.5 mag) is well fit by a standard King model with a central surface density of Sigma0 = 1.17 dEs arcmin-2 and a core radius Rc = 22.15 arcmin ( 0.46h-1 Mpc). This core is significantly larger than the Rc = 13.71 arcmin ( 0.29h-1 Mpc) found for the cluster giants and the brighter dEs (R ≤ 19.0 mag), again consistent with the idea that faint dEs in the dense core have been disrupted. Finally, we find that most dEs belong to the general Coma cluster potential rather than as satellites of individual giant galaxies: An analysis of the number counts around 10 cluster giants reveals that they each have on average 4± 1 dE companions within a projected radius of 13.9h-1 kpc.

A statistical investigation into the shape of the globular cluster luminosity distribution

Recent observations of the globular clusters in the Milky Way and M31 confirm that their luminosities follow a relatively simple distribution, the globular cluster luminosity function (GCLF), that is uni-modal and nearly symmetric. Maximum-likelihood methods are used to fit three simple types of analytic functions (Gaussian, Cauchy, and t) to the GCLFs in these two galaxies. The analytic function which best describes the GCLFs is found to be the t distribution with a shape parameter of μ ∼ 5

A maximum-likelihood analysis of globular cluster luminosity distributions in the Virgo ellipticals

We have formulated a model to represent globular cluster luminosity functions (GCLFs) in distant galaxies by means of maximum-likelihood statistics. This model simultaneously accounts for the presence of a contaminating background population, incompleteness at faint magnitudes, and photometric measurement error. We apply this model to observational data sets for the three Virgo giant elliptical galaxies NGC 4365, 4472, and 4649, to derive accurate new values for the GCLF peak and dispersion.

The Early-Type Dwarf-to-Giant Ratio and Substructure in the Coma Cluster

We have obtained new CCD photometry for a sample of

Constraints on the Hubble constant from observations of the brightest red-giant stars in a Virgo-cluster galaxy

\simeq 800

A RING MEDIAN FILTER FOR DIGITAL IMAGES

early-type galaxies (dwarf and giant ellipticals) in the central 700 arcmin

A Constraint on the Formation of Dwarf Elliptical Galaxies in the Dense Coma Cluster Core

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DEEP CCD PHOTOMETRY OF THE RICH GALAXY CLUSTER ABELL 1656 CHARACTERISTICS OF THE DWARF ELLIPTICAL GALAXY POPULATION IN THE CLUSTER CORE

of the Coma cluster, complete in color and in magnitude to

Interstellar transport and local-establishment dynamics of spaceborne propagules

R = 22.5

Washington photometry of the globular cluster system around NGC 3311. 1: Analysis of the metallicities

mag (