The Globular Cluster Systems in the Coma Ellipticals. IV: WFPC2 Photometry for Five Giant Ellipticals

We analyze photometric data in V and I for the globular cluster (GC) systems in five of the giant ellipticals in the Coma Cluster: NGC 4874, 4881, 4889, 4926, and IC 4051. All of the raw data, from the Hubble Space Telescope Wide Field Planetary Camera 2 Archive, are analyzed in a homogeneous way so that their five cluster systems can be strictly intercompared. We find that the GC luminosity functions are quite similar to one another and reinforce the common nature of the mass distribution of old, massive star clusters in gE galaxies. The globular cluster luminosity function (GCLF) turnover derived from a composite sample of more than 9,000 GCs appears at V = 27.71 ? 0.07 (MV = ?7.3), and our data reach about half a magnitude fainter than the turnover. We find that both a simple Gaussian curve and an evolved Schechter function fit the bright half of the GCLF equally well, though the Coma GCLF is broader and has a higher cutoff mass (Mc ~ 3 ? 106 M ?) than in any of the Virgo giants. These five Coma members exhibit a huge range in GC specific frequency, from a low of SN 0.7 for NGC 4881 up to 12 for IC 4051 and NGC 4874. No single formation scenario appears able to account for these differences in otherwise similar galaxies and may require carefully prescribed differences in their merger history, gas-free versus gas-rich progenitors, GC formation efficiency, initial density of environment, or tidal harassment within the Coma potential well. The supergiant cD galaxy NGC 4874 has the richest globular cluster system known, probably holding more than 30,000 clusters; its true extent is not yet determined and may extend well out into the Coma potential well. For the three biggest GC systems (NGC 4874, 4889, IC 4051), analysis of the (V ? I) color distributions shows that all three populations are dominated by red, metal-rich clusters. Their metallicity distributions also may all have the normal bimodal form, with the two sequences at mean colors V ? I(blue) 0.98 and V ? I(red) 1.15. These values fall along the previously established correlations of mean color with galaxy luminosity. However, the color distributions and relative numbers of metal-rich clusters show intriguing counterexamples to a trend established by Peng and colleagnes for the Virgo galaxies. For the brightest Virgo ellipticals, they find that the red GCs make up only ~30% of the cluster population, whereas in our similarly luminous Coma galaxies they make up more than half. At the very highest density and most massive regimes represented by the Coma supergiants, formation of metal-rich clusters seems to have been especially favored.