The XXL Survey. XXV. Cosmological analysis of the C1 cluster number counts

Abstract

Context. We present an estimation of cosmological parameters with clusters of galaxies. <BR /> Aims: We constrain the Ω<SUB>m</SUB>, σ<SUB>8</SUB>, and w parameters from a stand-alone sample of X-ray clusters detected in the 50 deg<SUP>2</SUP> XMM-XXL survey with a well-defined selection function. <BR /> Methods: We analyse the redshift distribution of a sample comprising 178 high signal-to-noise ratio clusters out to a redshift of unity. The cluster sample scaling relations are determined in a self-consistent manner. <BR /> Results: In a lambda cold dark matter (ΛCDM) model, the cosmology favoured by the XXL clusters compares well with results derived from the Planck Sunyaev-Zel'dovich clusters for a totally different sample (mass/redshift range, selection biases, and scaling relations). However, with this preliminary sample and current mass calibration uncertainty, we find no inconsistency with the Planck CMB cosmology. If we relax the w parameter, the Planck CMB uncertainties increase by a factor of 10 and become comparable with those from XXL clusters. Combining the two probes allows us to put constraints on Ω<SUB>m</SUB> = 0.316 ± 0.060, σ<SUB>8</SUB> = 0.814 ± 0.054, and w = -1.02 ± 0.20. <BR /> Conclusions: This first self-consistent cosmological analysis of a sample of serendipitous XMM clusters already provides interesting insights into the constraining power of the XXL survey. Subsequent analysis will use a larger sample extending to lower confidence detections and include additional observable information, potentially improving posterior uncertainties by roughly a factor of 3. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.