The Observations of Redshift Evolution in Large Scale Environments (ORELSE) Survey : I. The Survey Design and First Results on Cl 0023+0423 at z = 0.84 and RX J1821.6+6827 at z = 0.82

Details The Observations of Redshift Evolution in Large Scale Environments (ORELSE) Survey : I. The Survey Design and First Results on Cl 0023+0423 at z = 0.84 and RX J1821.6+6827 at z = 0.82 The Observations of Redshift Evolution in Large Scale Environments (ORELSE) Survey : I. The Survey Design and First Results on Cl 0023+0423 at z = 0.84 and RX J1821.6+6827 at z = 0.82

2008-09-11

arxiv.org/abs/0809.2092v2

Astronomy and Astrophysics

Astrophysics

47 pages, 12 figures, revised version accepted to AJ

Scientific paper

10.1088/0004-6256/137/6/4867

We present the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey, a systematic search for structure on scales greater than 10 Mpc around 20 well-known clusters at 0.6 < z < 1.3. We describe the survey design, the cluster sample, and our extensive observational data covering at least 25' 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 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 = 0.9. Here, we present the results on two additional clusters, Cl 0023+0423 at z = 0.84 and RX J1821.6+6827 at z = 0.82. The optically-selected Cl 0023+0423 is a four-way group-group merger with constituent groups having velocity dispersions between 206-479 km/s. The galaxy population is dominated by blue, star-forming galaxies, with a substantial contribution from recent starbursts. In contrast, the X-ray-selected RX J1821.6+6827 is a largely-isolated, massive cluster with a measured velocity dispersion of 926 +/- 77 km/s. 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. [Abridged]

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