The Bright SHARC Survey: The X-ray Cluster Luminosity Function

We present here initial results on the X-ray Cluster Luminosity Function (XCLF) from the Bright SHARC sample of distant X-ray clusters of galaxies. This sample is 97% complete in its optical identifications and contains 12 X-ray luminous clusters in the range 0.3 < z < 0.83 (median z = 0.42) and 1.1 < Lx(44) < 8.5 erg/s [0.5-2.0 keV]. We present a preliminary selection function for the Bright SHARC based on Monte Carlo simulations. Using this selection function, we have computed the Bright SHARC XCLF and find it to be fully consistent with a non-evolving XCLF to Lx(44) = 5 erg/s and z = 0.7. At Lx(44) > 5 erg/s, we find evidence for a deficit of clusters compared to that expected from a non-evolving XCLF. We detect only one such cluster in the redshift range 0.3 < z < 0.7 when we would expect 4.9 clusters based on the local XCLF of De Grandi et al. (1999). The statistical significance of this deficit is 96%. To increase the statistical significance of this possible deficit, we have combined the Bright SHARC and the 160 sq. deg. survey of Vikhlinin et al (1998a). This joint survey covers 260 sq. degs. and contains only one confirmed 0.3 < z < 0.7, Lx(44) > 5 erg/s cluster, while we would expect 7.6 such clusters based on the local XCLF (De Grandi et al. 1999). The statistical significance of the deficit in this joint survey increases to 99.5%. These results remain preliminary because of incompletenesses in the optical follow-up and uncertainties in the local XCLF.