Galactic Dark Matter Halos and Globular Cluster Populations. III:
  Extension to Extreme Environments
  The total mass M_GCS in the globular cluster (GC) system of a galaxy is
empirically a near-constant fraction of the total mass M_h = M_bary + M_dark of
the galaxy, across a range of 10^5 in galaxy mass. This trend is radically
unlike the strongly nonlinear behavior of total stellar mass M_star versus M_h.
We discuss extensions of this trend to two more extreme situations: (a) entire
clusters of galaxies, and (b) the Ultra-Diffuse Galaxies (UDGs) recently
discovered in Coma and elsewhere. Our calibration of the ratio \eta_M = M_GCS /
M_h from normal galaxies, accounting for new revisions in the adopted
mass-to-light ratio for GCs, now gives \eta_M = 2.9 \times 10^{-5} as the mean
absolute mass fraction. We find that the same ratio appears valid for galaxy
clusters and UDGs. Estimates of \eta_M in the four clusters we examine tend to
be slightly higher than for individual galaxies, butmore data and better
constraints on the mean GC mass in such systems are needed to determine if this
difference is significant. We use the constancy of \eta_M to estimate total
masses for several individual cases; for example, the total mass of the Milky
Way is calculated to be M_h = 1.1 \times 10^{12} M_sun. Physical explanations
for the uniformity of \eta_M are still descriptive, but point to a picture in
which massive, dense star clusters in their formation stages were relatively
immune to the feedback that more strongly influenced lower-density regions
where most stars form.
