Observations of a Distant Luminous Cluster of Galaxies

A key to understanding cluster evolution is to study distant clusters ofgalaxiesin Xrays. We propose to observe with Chandra, XMMNewton, and Spitzer CL1257(Cl J1257+4738). CL1257 is the most distant (z0.866) cluster found in the SHARCsurvey and the second most Xray luminous cluster above z0.85. The data willhelp to determine the global physical properties of CL1257 and its globaldynamical state. With recent Gemini data we found 4 out of 6 cluster membergalaxies to have OII 3727 emission lines, implying recent starburst activity.A compilation of luminosity versus redshift of known clusters above z0.85suggests that clusters do not reach their peak Xray luminosity until z0.9. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]