The X-Ray Luminosity Function of Nearby Rich and Poor Clusters of Galaxies:A Cosmological Probe

In this Letter, we present a new determination of the local (z · 0.09) X-ray luminosity function (XLF) using a large, statistical sample of 294 Abell clusters and the ROSAT All-Sky Survey. Despite the optical selection of this catalog, we find excellent agreement with other recent determinations of the local XLF. Given our large sample size, we have reduced errors by nearly a factor of 2 for L ¸ 1043 h22 ergs s21. We combine our X(0.5-2.0 keV) 50 data with previous work to produce the most tightly constrained local determination of the XLF (over 3 orders of magnitude in LX) in order to explore possible constraints imposed by the shape of the XLF on cosmological models. A set of currently viable cosmologies is used to construct theoretical XLFs assuming L / Mp and a j8-Q0 constraint based on the local X-ray temperature function. We fit these models to our observed XLF and verify that the simplest adiabatic, analytic scaling relation disagrees strongly with observations. If we assume that clusters can be described by the preheated, constant core entropy models of Evrard & Henry, then the observed XLF is consistent only with 0.1 ! Q ! 0.4 if the energy per unit mass in galaxies is roughly equal to 0 the gas energy (i.e., if b » 1).This work was supported in part by NASA grants NAG5-6739 and NAGW-3152 and NSF grant AST-9896039