We present the Observations of Redshift Evolution in Large Scale Environments ( ORELSE ) survey , a systematic search for structure on scales greater than 10 h _ { 70 } ^ { -1 } Mpc around 20 well-known clusters at redshifts of 0.6 < z < 1.3 .
The goal of the survey is to examine a statistical sample of dynamically active clusters and large scale structures in order to quantify galaxy properties over the full range of local and global environments .
We describe the survey design , the cluster sample , and our extensive observational data covering at least 25 ^ { \prime } around each target cluster .
We use adaptively-smoothed red galaxy density maps from our wide-field optical imaging to identify candidate groups/clusters and intermediate-density large scale filaments/walls in each cluster field .
Because photometric techniques ( such as photometric redshifts , statistical overdensities , and richness estimates ) can be highly uncertain , the crucial component of this survey is the unprecedented amount of spectroscopic coverage .
We are using the wide-field , multi-object spectroscopic capabilities of the DEep Multi-Object Imaging Spectrograph to obtain 100-200+ confirmed cluster members in each field .
Our survey has already discovered the Cl 1604 supercluster at z \approx 0.9 , a structure which contains at least eight groups and clusters and spans 13 Mpc \times 100 Mpc .
Here , we present the results on the large scale environments of two additional clusters , Cl 0023+0423 at z = 0.84 and RX J1821.6+6827 at z = 0.82 , which highlight the diversity of global properties at these redshifts .
The optically–selected Cl 0023+0423 is a four-way group-group merger with constituent groups having measured velocity dispersions between 206–479 km s ^ { -1 } .
The galaxy population is dominated by blue , star-forming galaxies , with 80 % of the confirmed members showing [ OII ] emission .
The strength of the H \delta line in a composite spectrum of 138 members indicates a substantial contribution from recent starbursts to the overall galaxy population .
In contrast , the X-ray–selected RX J1821.6+6827 is a largely-isolated , massive cluster with a measured velocity dispersion of 926 \pm 77 km s ^ { -1 } .
The cluster exhibits a well defined red sequence with a large quiescent galaxy population .
The results from these two targets , along with preliminary findings on other ORELSE clusters , suggest that optical selection may be more effective than X-ray surveys at detecting less-evolved , dynamically-active systems at these redshifts .