F. Pacaud, M. Pierre, J.-B. Melin, C. Adami, A. E. Evrard, S. Galli, F. Gastaldello, B. J. Maughan, M. Sereno, S. Alis, B. Altieri, M. Birkinshaw, L. Chiappetti, L. Faccioli, P. A. Giles, C. Horellou, A. Iovino, E. Koulouridis, J.-P. Le Fèvre, C. Lidman, M. Lieu, S. Maurogordato, L. Moscardini, B. M. Poggianti, E. Pompei, T. Sadibekova, I. Valtchanov, J. P. Willis
A&A Volume 620, December 2018 The XXL Survey: second series
Publication year: 2018


Context. We present an estimation of cosmological parameters with clusters of galaxies.

Aims. We constrain the Ωmσ8, and w parameters from a stand-alone sample of X-ray clusters detected in the 50 deg2 XMM-XXL survey with a well-defined selection function.

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.

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 Ωm = 0.316 ± 0.060, σ8 = 0.814 ± 0.054, and w = −1.02 ± 0.20.

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.