The [ITAL]ROSAT[/ITAL] Deep Cluster Survey: The X-Ray Luminosity Function out to [CLC][ITAL]z[/ITAL][/CLC] = 0.8

Abstract

We present the X-ray luminosity function (XLF) of the ROSAT Deep Cluster Survey sample over the redshift range 0.05-0.8. Our results are derived from a complete flux-limited subsample of 70 galaxy clusters, representing the brightest half of the total sample, which have been spectroscopically identified down to the flux limit of 4×10 -->−14 ergs m-2 s-1 (0.5-2.0 keV) and have been selected via a serendipitous search in ROSAT PSPC pointed observations. The redshift baseline is large enough that evolutionary effects can be studied within the sample. The local XLF (z≤0.25) is found to be in excellent agreement with previous determinations using ROSAT All-Sky Survey data. The XLF at higher redshifts, when combined with the deepest number counts constructed to date (f>2×10 -->−14 ergs cm -->−2 s -->−1), reveals no significant evolution at least out to z=0.8, over a luminosity range of 2 × 1042 to 3 × 1044 ergs s -->−1 in the 0.5-2 keV band. These findings extend the study of cluster evolution to the highest redshifts and the faintest fluxes probed so far in X-ray surveys. They complement and do not necessarily conflict with those of the Einstein Extended Medium-Sensitivity Survey, leaving open the possibility of negative evolution of the brightest end of the XLF at high redshifts.