Measuring Ω m with the ROSAT Deep Cluster Survey

Abstract

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 Ñux limit ergs s~1 cm~2 (RDCS-3) in the [0.5È2.0] keV energy band, F lim \ 3 ] 10~14 with a high-redshift extension containing four clusters at 0.90 ¹ z ¹ 1.26 and brighter than F lim \ 1 ] 10~14 ergs s~1 cm~2 (RDCS-1). We assume cosmological models to be speciÐed by the matter density parameter the rms Ñuctuation amplitude at the 8 h~1 Mpc scale and the shape parameter for the) m , p 8 , cold dark matterÈlike power spectrum !. Model predictions for the cluster mass function are converted into the X-ray luminosity function in two steps. First, we convert mass into intracluster gas temperature by assuming hydrostatic equilibrium. Then, temperature is converted into X-ray luminosity by using the most recent data on the relation for nearby and distant clusters. These include the Chandra data L X-T X for six distant clusters at 0.57 ¹ z ¹ 1.27. From RDCS-3 we Ðnd and) m \ 0.35 ~0.10`0 10`0.13 p 8 \ for a spatially Ñat universe with a cosmological constant, with no signiÐcant constraint on ! 0.66 ~0.05`0 05`0.06 (errors correspond to 1 p conÐdence levels for three Ðtting parameters). Even accounting for both theoretical and observational uncertainties in the massÈX-ray luminosity conversion, an EinsteinÈde Sitter model is always excluded at far more than the 3 p level. We also show that the number of X-rayÈbright clusters in RDCS-1 at z [ 0.9 is expected from the evolution inferred at z \ 0.9 data.