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

Jeff Secker, William E. Harris and Julia D. Plummer
Publications of the Astronomical Society of the Pacific
Vol. 109, No. 742 (1997 December), pp. 1377-1393
Stable URL: http://www.jstor.org/stable/40681047
Page Count: 17
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Dwarf Galaxies in the Coma Cluster. II. Photometry and Analysis
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Abstract

We use the dataset derived in our previous paper (Secker and 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 [Δ(B-R)/ΔR = –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 α = -1.41 ± 0.05. This value of α is consistent with those measured for the Virgo and Fornax clusters. The spatial distribution of the faint dE galaxies (19.0c = 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 ten cluster giants reveals that they each have on average 4 ± 1 dE companions within a projected radius of 13.9h⁻¹ kpc.

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