Absolute V-band magnitudes and mass-to-light ratios of Galactic globular
  clusters
  We have used HST and ground-based photometry to determine total $V$-band
magnitudes and mass-to-light ratios of more than 150 Galactic globular
clusters. We do this by summing up the magnitudes of their individual member
stars, using color-magnitude information, Gaia DR2 proper motions and radial
velocities to distinguish cluster stars from background stars. Our new
magnitudes confirm literature estimates for bright clusters with V<8, but can
deviate by up to two magnitudes from literature values for fainter clusters.
They lead to absolute mass-to-light ratios that are confined to the narrow
range 1.4<M/L_V<2.5, significantly smaller than what was found before. We also
find a correlation between a cluster's M/L_V value and its age, in agreement
with theoretical predictions. The M/L_V ratios of globular clusters are also in
good agreement with those predicted by stellar isochrones, arguing against a
significant amount of dark matter inside globular clusters. We finally find
that, in agreement with what has been seen in M31, the magnitude distribution
of outer halo globular clusters has a tail towards faint clusters that is
absent in the inner parts of the Milky Way.
