THE LUMINOSITY-TEMPERATURE RELATION AT Z=0.4 FOR CLUSTERS OF GALAXIES

We have obtained the first large sample of accurate temperatures for c lusters at z > 0.14 from ASCA. We compare the luminosity-temperature ( L-T) distribution for these clusters with the low-redshift sample of D avid and coworkers and find that there is no evidence for evolution. W e also find that the intrinsic variance in this relation is roughly co nstant with redshift. Additionally, there is no detectable change in t he relationship of optical velocity dispersion to X-ray temperature wi th redshift. Most cosmological simulations driven primarily by gravity predict substantial changes in the L-T relation due to the recent rap id growth of clusters. Our results are consistent either with models i n which the cluster core entropy is dominated by preheating, or with l ow-Omega models in which cluster structure does not evolve strongly wi th time. The intrinsic variance in the L-T relation at a fixed redshif t can be due to variety of possible causes, e.g., a change in the bary onic fraction from cluster to cluster, variation in the fraction of th e total energy in the system arising from shocks or supernova heating, or variations in the emission measure distributions in multiphase gas .