MEASURING M WITH THE ROSAT DEEP CLUSTER SURVEY

We analyze the ROSAT Deep Cluster Survey (RDCS) to derive cosmological constraints from the evolution of the cluster X-ray luminosity distribution. The sample contains 103 galaxy clusters out to z ≃ 0.85 and flux-limit Flim = 3 × 10−14 ergs−1cm−2 (RDCS-3) in the (0.5-2.0) keV energy band, with a high-redshift extension containing four clusters at 0.90 ≤ z ≤ 1.26 and brighter than Flim = 1 × 10−14 ergs−1cm−2 (RDCS-1). We assume cosmological models to be specified by the mat- ter density parameter m, the r.m.s. fluctuation amplitude at the 8 h−1Mpc scale σ8, and the shape parameter for the CDM-like power spectrum . Model predicti ons for the cluster mass function are converted into the X-ray luminosity function in two steps. First we convert mass into intra-cluster gas temperature by assuming hydrostatic equilibrium. Then temperature is converted into X-ray luminosity by using the most recent data on the LX-TX relation for nearby and distant clusters. These include the Chandra data for seven distant clusters at 0.57 ≤ z ≤ 1.27. From RDCS-3 we find m = 0.35+0.13 −0.10 and σ8 = 0.66 +0.06 −0.05 for a spatially flat Universe with cosmological constant, with no significant constraint on (errors correspond to 1 σ confidence levels for three fitting parameters). Even accounting for both the- oretical and observational uncertainties in the mass-X-ray luminosity conversion, an Einstein-de-Sitter model is always excluded at far more than the 3σ level. We also show that the number of X-ray bright clusters in RDCS-1 at z > 0.9 are expected from the evolution inferred at z < 0.9 data. Subject headings: Cosmology: theory - dark matter - galaxies: clusters: general - X-rays: galaxies