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Session 102 - Clusters of Galaxies.
Display session, Thursday, January 16
Clusters of galaxies are the largest gravitationally bound structures in the universe and are laboratories for studying galaxy formation and evolution as well as for measuring cosmological parameters. Thousands of clusters have been identified at redshifts z\le 0.25 but when we reach z\ge 0.5 the number of clusters with spectroscopically determined redshifts dwindles to eighteen. We are employing an efficient new technique for generating a sample of >100 new clusters (most at high-z). We begin with a sample of \sim 250 bent double radio galaxies derived from the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey currently underway at the VLA (Becker, White, amp; Helfand 1995). The distinctive morphology of these sources arises from the ram-pressure deflection of the radio jets by the relative motion of a dense intracluster medium and the host galaxy. Our sample consists mostly of low-power (P < 10^25 W Hz^-1) FR I sources which are detectable to z\approx 2 at 10 mJy (70\sigma) in FIRST. We will present follow-up R-band images (KPNO 2.1m and 4m) taken at the positions of several dozen radio galaxies in our sample which reveal obvious, rich clusters out to z\approx 1. Weather permitting, results will be presented from our Keck II multi-slit mask spectroscopy run (December 1996). These data will confirm our cluster identifications and provide redshifts, significantly augmenting the number of known high-z clusters.
The FIRST project is supported by grants from the National Geographic Society, the National Science Foundation, NATO, IGPP, Columbia University, and Sun Microsystems.
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