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Session 53 - Surveys of Galaxies & Clusters.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center

[53.01] The Palomar Distant Cluster Survey

M. Postman (STScI), L. Lubin (OCIW), J. Gunn (Princeton U.), J. B. Oke (DAO), J. Hoessel (U. Wisconsin), D. Schneider (PSU), J. Christensen (STScI)

We present an optical/near IR selected catalog of 79 clusters distributed over an area of 5.1 square degrees. The catalog was constructed from images obtained with the 4-Shooter CCD mosaic camera on the Hale 5m telescope operating in ``scan" mode. The survey, hereafter known as the Palomar Distant Cluster Survey (PDCS), was conducted in two broad band filters that closely resemble V and I. The 4\sigma limiting magnitudes for our 300 s exposures are \sim 23.8 (V) and 22.5 (I). A matched filter algorithm was developed and employed to identify the cluster candidates by using positional and photometric data simultaneously. The clusters cover the range 0.2 \le z \le 1.2, based on the redshift estimates derived in the cluster detection procedure. An accurate selection function is generated from extensive simulations. We find that the cumulative surface density of clusters with richness class R \ge 1 is about a factor of 5 higher than the extrapolated density of R \ge 1 Abell clusters. The PDCS results are consistent with a constant comoving density of clusters to z \le 0.6, albeit at the above high density level. Constraints on cluster abundances at z > 0.6 will be possible with the acquisition of spectroscopic redshifts for a large subset of these cluster candidates. We also present a supplemental catalog of 28 clusters that do not satisfy all our selection criteria but which include some of the most distant systems detected in the survey.

We have analyzed the richest clusters in this sample and find that the typical cluster has a surface density profile of r^-1.4 (r \ge 0.15 h^-1 Mpc) and a core radius of 0.1 h^-1 Mpc. We see some evidence that the slope of the surface density profile steepens with increasing redshift. Our cluster population is inconsistent at a 99.2% confidence level with a population of azimuthally symmetric clusters.

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