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[10.11] The Stanford Cluster Search (StaCS): Towards an Unbiased Sample of Rich Clusters at Intermediate Redshift

J.A. Willick, K.L. Thompson (Stanford University)

We describe StaCS, a program to identify intermediate redshift (0.3 \le z \le 1.0) rich clusters of galaxies from deep, wide- field CCD images, and to follow-up these identifications with extensive spectroscopy at the Hobby-Eberly Telescope (HET). The clusters are identified using a matched-filter algorithm applied to images acquired as part of the Lawrence Berkeley Laboratory Supernova Cosmology Project (SCP). The SCP imaging data base covers approximately 25 square degrees of sky to a depth m_R= 23.5 or fainter. Follow-up observations from the 8 meter class HET will measure cluster redshifts and velocity dispersions. The velocity dispersions will in turn yield mass estimates, which we will seek to confirm with future X-ray and gravitational lensing measurements. Our measurements will enable us to determine the comoving number density of clusters as a function of mass and redshift, n(M,z). Comparison with theoretical predictions, from the Press-Schechter formalism and related approaches, will allow a determination of the mass density parameter \Omega_M, and the rms density fluctuation on an 8 Mpc scale, \sigma₈, to 15% accuracy or better, and a test of the hypothesis that the primordial density fluctuations are Gaussian. In a companion poster (Thompson & Willick), we describe the first spectroscopic results from the HET.

This work is supported in part by the Research Corporation.

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