The Globular Cluster Systems in the Coma Ellipticals. III. The Unique Case of IC 4051

Abstract

IC 4051 is a giant E galaxy on the outskirts of the Coma Cluster core. Using archival HST WFPC2 data, we derive the metallicity distribution, luminosity function, and spatial structure of its globular cluster system (GCS). The metallicity distribution derived from the V-I colors has a mean Fe/H -0.3, a near-complete lack of metal-poor clusters, and only a small metallicity gradient with radius. We tentatively suggest that the GCS has two roughly equal metallicity subcomponents, one centered at [Fe/H] ~ 0.0 and the second at [Fe/H] ~ -1.0, although their identification is blurred by the photometric uncertainties. The luminosity distribution (globular cluster luminosity function) has the standard Gaussian-like form observed in all other giant E galaxies, with a peak (turnover) at V0 = 27.8, consistent with a Coma distance of 100 Mpc. The radial profiles of both the GCS and the halo light show an unusually steep falloff, which may indicate that the halo of this galaxy has been tidally truncated. Lastly, the specific frequency of the GCS is remarkably large: we find SN = 11 ? 2, at a level that rivals M87 and most others in the central cD-type category, even though IC 4051 is not a cD or brightest cluster elliptical. This galaxy exhibits a combination of GCS characteristics found nowhere else. A formation model consistent with most of the observations would be that this galaxy was subjected to removal of a large fraction of its protogalactic gas shortly after its main phase of globular cluster formation, probably by its first passage through the Coma core. Since then, no significant additions due to accretions or mergers have taken place, in strong contrast to the central Coma galaxy NGC 4874.