Cosmological constraints from the ROSAT Deep Cluster Survey

The ROSAT Deep Cluster Survey (RDCS) has provided a new large deep sample of X-ray selected galaxy clusters. Observables such as the nux number counts n(S), the redshift distribution n(z), and the X-ray luminosity function (XLF) over a large redshift baseline (,z less than or similar to 0.8) are used here in order to constrain cosmological models. Our analysis is based on the Press-Schechter approach, whose reliability is tested against N-body simulations. Following a phenomenological approach, no assumption is made a priori on the relation between cluster masses and observed X-ray luminosities. As a first step, we use the local XLF from RDCS, along with the high-luminosity extension provided by the XLF from the Brightest Cluster Survey, in order to constrain the amplitude of the power spectrum, a,, and the shape of the local luminosity-temperature, L-bol-T, relation. We obtain sigma(8) = (0.58 +/- 0.06) x Omega(0)(-0.47+0.16 Ohm 0) for flat models (Omega(Lambda) = 1 - Omega(0)) and sigma(8) = (0.58 +/- 0.06) x Omega(0)(-0.53+0.27 Ohm 0) for open models (Omega(Lambda) = 0) at a 90% confidence level, almost independent of the L-bol-T shape. The density parameter Omega(0) and the evolution of the L-bol-T relation are constrained by the RDCS XLF at z > 0 and the EMSS XLF at (z) over bar = 0.33, and by the RDCS n(S) and n(z) distributions. By modeling the evolution for the amplitude of the L-bol-T relation as (1 + z)(A), an Omega(0) = 1 model can be accommodated for the evolution of the XLF with 1 less than or equal to A less than or equal to 3 at a 90% confidence level, while Omega(0) = 0.4(-0.2)(+0.3) and Omega(0) less than or similar to 0.6 are implied by a nonevolving L-bol-T (A = 0) for open and flat models, respectively.