A Systematic Analysis of Caustic Methods for Galaxy Cluster Masses
  We quantify the expected observed statistical and systematic uncertainties of
the escape velocity as a measure of the gravitational potential and total mass
of galaxy clusters. We focus our attention on low redshift (z < 0.15) clusters,
where large and deep spectroscopic datasets currently exist. Utilizing a suite
of Millennium Simulation semi-analytic galaxy catalogs, we find that the
dynamical mass, as traced by either the virial relation or the escape velocity,
is robust to variations in how dynamical friction is applied to "orphan"
galaxies in the mock catalogs (i.e., those galaxies whose dark matter halos
have fallen below the resolution limit). We find that the caustic technique
recovers the known halo masses (M_200) with a third less scatter compared to
the virial masses. The bias we measure increases quickly as the number of
galaxies used decreases. For N_gal > 25, the scatter in the escape velocity
mass is dominated by projections along the line-of-sight. Algorithmic
uncertainties from the determination of the projected escape velocity profile
are negligible. We quantify how target selection based on magnitude, color, and
projected radial separation can induce small additional biases into the escape
velocity masses. Using N_gal = 150 (25), the caustic technique has a per
cluster scatter in ln(M|M_200) of 0.3 (0.5) and bias 1+/-3% (16+/-5%) for
clusters with masses > 10^14M_solar at z<0.15.
