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 Serendipitous High-Redshift Archival Cluster (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 redshift range 0.3 ≤ z ≤ 0.83 (median z = 0.42) and 1.1 × 10⁴⁴ ≤ L_x ≤ 8.3 × 10⁴⁴ ergs s^-1 (0.5-2.0 keV). We present a preliminary selection function for the Bright SHARC Survey based on Monte Carlo simulations. Using this selection function, we have computed the Bright SHARC Survey XCLF and find it to be fully consistent with a nonevolving XCLF to L_x ≃ 5 × 10⁴⁴ ergs s^-1 and z ≃ 0.7. At L_x > 5 × 10⁴⁴ ergs s^-1, we find evidence for a deficit of clusters compared to that expected from a nonevolving 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. The statistical significance of this deficit is ≃96%. To increase the statistical significance of this possible deficit, we have combined the Bright SHARC Survey and the 160 deg² survey of Vikhlinin et al. This joint survey covers ≃260 deg² and contains only one confirmed 0.3 ≤ z ≤ 0.7, L_x > 5 × 10⁴⁴ ergs s^-1 cluster, while we would expect 7.6 such clusters based on the local XCLF (De Grandi et al.). 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.