We present galaxy velocity dispersions and dynamical mass estimates for 44 galaxy clusters selected via the Sunyaev-Zel ’ dovich ( SZ ) effect by the Atacama Cosmology Telescope .
Dynamical masses for 18 clusters are reported here for the first time .
Using N-body simulations , we model the different observing strategies used to measure the velocity dispersions and account for systematic effects resulting from these strategies .
We find that the galaxy velocity distributions may be treated as isotropic , and that an aperture correction of up to 7 per cent in the velocity dispersion is required if the spectroscopic galaxy sample is sufficiently concentrated towards the cluster centre .
Accounting for the radial profile of the velocity dispersion in simulations enables consistent dynamical mass estimates regardless of the observing strategy .
Cluster masses M _ { 200 } are in the range ( 1 - 15 ) \times 10 ^ { 14 } M _ { \odot } .
Comparing with masses estimated from the SZ distortion assuming a gas pressure profile derived from X-ray observations gives a mean SZ-to-dynamical mass ratio of 1.10 \pm 0.13 , but there is an additional 0.14 systematic uncertainty due to the unknown velocity bias ; the statistical uncertainty is dominated by the scatter in the mass-velocity dispersion scaling relation .
This ratio is consistent with previous determinations at these mass scales .