Investigating the M GCS-M h Relation in the Most Massive Galaxies

The relation between the total mass contained in the globular clusters of a galaxy and the mass of its dark-matter halo has been found observationally to be nearly linear over five decades of mass. However, the high-mass end of this relation is not well determined from previous data and shows large scatter. We analyze the globular cluster systems (GCSs) of a homogeneous sample of 11 brightest cluster galaxies (BCGs) through DOLPHOT photometry of their deep Hubble Space Telescope images in the F814W filter. We standardize the definition of M _GCS, the total GCS mass, by using the GC total population within a limiting radius of 0.1R _virial, while the dark-matter halo mass M _h is determined from the weak-lensing calibration of M _h versus M _bary. When these 11 BCGs are added to the previously studied homogeneous catalog of Virgo member galaxies, a total value for η = M _GCS/M _h is found to be (3.0 ± 1.8_internal) × 10^-5, slightly higher than previous estimates but with much reduced uncertainty. Perhaps more importantly, the results suggest that the relation continues to have a near-linear shape at the highest galaxy masses, strongly reinforcing the conclusion that accreted GCs make a major contribution to the GC populations at high galaxy mass.