We present dynamical distance estimates for 15 Galactic globular clusters and use these to check the consistency of dynamical and photometric distance estimates .
For most of the clusters , this is the first dynamical distance estimate ever determined .
We extract proper-motion dispersion profiles using cleaned samples of bright stars from the Hubble Space Telescope proper-motion catalogs recently presented in and compile a set of line-of-sight velocity-dispersion profiles from a variety of literature sources .
Distances are then estimated by fitting spherical , non-rotating , isotropic , constant mass-to-light ( M/L ) dynamical models to the proper-motion and line-of-sight dispersion profiles together .
We compare our dynamical distance estimates with literature photometric estimates from the , 2010 edition globular cluster catalog and find that the mean fractional difference between the two types is consistent with zero at just -1.9 \pm 1.7 \% .
This indicates that there are no significant biases in either estimation method and provides an important validation of the stellar-evolution theory that underlies photometric distance estimates .
The analysis also estimates dynamical M/L ratios for our clusters ; on average , the dynamically-inferred M/L ratios agree with existing stellar-population-based M/L ratios that assume a Chabrier initial mass function ( IMF ) to within -8.8 \pm 6.4 \% , implying that such an IMF is consistent with our data .
Our results are also consistent with a Kroupa IMF , but strongly rule out a Salpeter IMF .
We detect no correlation between our M/L offsets from literature values and our distance offsets from literature values , strongly indicating that our methods are reliable and our results are robust .