Globular Cluster Systems in Brightest Cluster Galaxies: A Near-Universal
  Luminosity Function?
  We present the first results from our HST Brightest Cluster Galaxy (BCG)
survey of seven central supergiant cluster galaxies and their globular cluster
(GC) systems. We measure a total of 48000 GCs in all seven galaxies,
representing the largest single GC database. We find that a log-normal shape
accurately matches the observed luminosity function (LF) of the GCs down to the
GCLF turnover point, which is near our photometric limit. In addition, the LF
has a virtually identical shape in all seven galaxies. Our data underscore the
similarity in the formation mechanism of massive star clusters in diverse
galactic environments. At the highest luminosities (log L > 10^7 L_Sun) we find
small numbers of "superluminous" objects in five of the galaxies; their
luminosity and color ranges are at least partly consistent with those of UCDs
(Ultra-Compact Dwarfs). Lastly, we find preliminary evidence that in the outer
halo (R > 20 kpc), the LF turnover point shows a weak dependence on projected
distance, scaling as L_0 ~ R^-0.2, while the LF dispersion remains nearly
constant.
