We present a detection-significance-limited catalog of 21 Sunyaev-Zel ’ dovich-selected galaxy clusters .
These clusters , along with 1 unconfirmed candidate , were identified in 178 deg ^ { 2 } of sky surveyed in 2008 by the South Pole Telescope to a depth of 18 \mu K-arcmin at 150 GHz .
Optical imaging from the Blanco Cosmology Survey ( BCS ) and Magellan telescopes provided photometric ( and in some cases spectroscopic ) redshift estimates , with catalog redshifts ranging from z = 0.15 to z > 1 , with a median z = 0.74 .
Of the 21 confirmed galaxy clusters , three were previously identified as Abell clusters , three were presented as SPT discoveries in , and three were first identified in a recent analysis of BCS data by ; the remaining 12 clusters are presented for the first time in this work .
Simulated observations of the SPT fields predict the sample to be nearly 100 % complete above a mass threshold of M _ { 200 } \approx 5 \times 10 ^ { 14 } M _ { \odot } h ^ { -1 } at z = 0.6 .
This completeness threshold pushes to lower mass with increasing redshift , dropping to \sim 4 \times 10 ^ { 14 } M _ { \odot } h ^ { -1 } at z = 1 .
The size and redshift distribution of this catalog are in good agreement with expectations based on our current understanding of galaxy clusters and cosmology .
In combination with other cosmological probes , we use this cluster catalog to improve estimates of cosmological parameters .
Assuming a standard spatially flat wCDM cosmological model , the addition of our catalog to the WMAP 7-year results yields \sigma _ { 8 } = 0.81 \pm 0.09 and w = -1.07 \pm 0.29 , a \sim 50 \% improvement in precision on both parameters over WMAP7 alone .