Cosmological Constraints from theROSATDeep Cluster Survey

Abstract

The ROSAT Deep Cluster Survey (RDCS) has provided a new large deep sample of X-ray selected galaxy clusters. Observables such as the flux number counts n(S), the redshift distribution n(z), and the X-ray luminosity function (XLF) over a large redshift baseline (z≲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, σ8, and the shape of the local luminosity-temperature, Lbol-T, relation. We obtain σ8=(0.58 ± 0.06) × Ω0-0.47+0.16Ω for flat models (ΩΛ=1-Ω0) and σ8=(0.58 ± 0.06) × Ω0-0.53+0.27Ω for open models (ΩΛ=0) at a 90% confidence level, almost independent of the Lbol-T shape. The density parameter Ω0 and the evolution of the Lbol-T relation are constrained by the RDCS XLF at z>0 and the EMSS XLF at =0.33, and by the RDCS n(S) and n(z) distributions. By modeling the evolution for the amplitude of the Lbol-T relation as (1+z)A, an Ω0=1 model can be accommodated for the evolution of the XLF with 1≲A≲3 at a 90% confidence level, while Ω0=0.4+0.3−0.2 and Ω0≲0.6 are implied by a nonevolving Lbol-T (A=0) for open and flat models, respectively.