SPT-GMOS: A Gemini/GMOS-South Spectroscopic Survey of Galaxy Clusters in
  the SPT-SZ Survey
  We present the results of SPT-GMOS, a spectroscopic survey with the Gemini
Multi-Object Spectrograph (GMOS) on Gemini South. The targets of SPT-GMOS are
galaxy clusters identified in the SPT-SZ survey, a millimeter-wave survey of
2500 squ. deg. of the southern sky using the South Pole Telescope (SPT).
Multi-object spectroscopic observations of 62 SPT-selected galaxy clusters were
performed between January 2011 and December 2015, yielding spectra with radial
velocity measurements for 2595 sources. We identify 2243 of these sources as
galaxies, and 352 as stars. Of the galaxies, we identify 1579 as members of
SPT-SZ galaxy clusters. The primary goal of these observations was to obtain
spectra of cluster member galaxies to estimate cluster redshifts and velocity
dispersions. We describe the full spectroscopic dataset and resulting data
products, including galaxy redshifts, cluster redshifts and velocity
dispersions, and measurements of several well-known spectral indices for each
galaxy: the equivalent width, W, of [O II] 3727,3729 and H-delta, and the 4000A
break strength, D4000. We use the spectral indices to classify galaxies by
spectral type (i.e., passive, post-starburst, star-forming), and we match the
spectra against photometric catalogs to characterize spectroscopically-observed
cluster members as a function of brightness (relative to m*). Finally, we
report several new measurements of redshifts for ten bright, strongly-lensed
background galaxies in the cores of eight galaxy clusters. Combining the
SPT-GMOS dataset with previous spectroscopic follow-up of SPT-SZ galaxy
clusters results in spectroscopic measurements for >100 clusters, or ~20% of
the full SPT-SZ sample.
