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 WFPC2 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 GCLF turnover derived from a composite sample of more than 9 , 000 GCs appears at V = 27.71 \pm 0.07 ( M _ { V } = -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 ” ( M _ { c } \sim 3 \times 10 ^ { 6 } M _ { \odot } ) than in any of the Virgo giants .
These five Coma members exhibit a huge range in GC specific frequency , from a low of S _ { N } \simeq 0.7 for NGC 4881 up to \simeq 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 \langle V - I \rangle ( blue ) \simeq 0.98 and \langle V - I \rangle ( red ) \simeq 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 et al .
2008 ( ApJ 681 , 197 ) for the Virgo galaxies .
For the brightest Virgo ellipticals , they find that the red GCs make up only \sim 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 .