# The XXL Survey. II. The bright cluster sample: catalogue and luminosity function

Pacaud, F and Clerc, N and Giles, PA and Adami, C and Sadibekova, T and Pierre, M and Maughan, BJ and Lieu, M and Fèvre, J-PL and Alis, S and Altieri, B and Ardila, F and Baldry, IK and Benoist, C and Birkinshaw, M and Chiappetti, L and Démoclès, J and Eckert, D and Evrard, AE and Faccioli, L and Gastaldello, F and Guennou, L and Horellou, C and Iovino, A and Koulouridis, E and Brun, VL and Lidman, C and Liske, J and Maurogordato, S and Menanteau, F and Owers, M and Poggianti, B and Pomarède, D and Pompei, E and Ponman, TJ and Rapetti, D and Reiprich, TH and Smith, GP and Tuffs, R and Valageas, P and Valtchanov, I and Willis, JP and Ziparo, F (2015) The XXL Survey. II. The bright cluster sample: catalogue and luminosity function. Astronomy & Astrophysics. ISSN 1432-0746

Context. The XXL Survey is the largest survey carried out by the XMM-Newton satellite and covers a total area of 50 square degrees distributed over two fields. It primarily aims at investigating the large-scale structures of the Universe using the distribution of galaxy clusters and active galactic nuclei as tracers of the matter distribution. Aims. This article presents the XXL bright cluster sample, a subsample of 100 galaxy clusters selected from the full XXL catalogue by setting a lower limit of $3\times 10^{-14}\,\mathrm{erg \,s^{-1}cm^{-2}}$ on the source flux within a 1$^{\prime}$ aperture. Methods. The selection function was estimated using a mixture of Monte Carlo simulations and analytical recipes that closely reproduce the source selection process. An extensive spectroscopic follow-up provided redshifts for 97 of the 100 clusters. We derived accurate X-ray parameters for all the sources. Scaling relations were self-consistently derived from the same sample in other publications of the series. On this basis, we study the number density, luminosity function, and spatial distribution of the sample. Results. The bright cluster sample consists of systems with masses between $M_{500}=7\times 10^{13}$ and $3\times 10^{14} M_\odot$, mostly located between $z=0.1$ and 0.5. The observed sky density of clusters is slightly below the predictions from the WMAP9 model, and significantly below the predictions from the Planck 2015 cosmology. In general, within the current uncertainties of the cluster mass calibration, models with higher values of $\sigma_8$ and/or $\Omega_m$ appear more difficult to accommodate. We provide tight constraints on the cluster differential luminosity function and find no hint of evolution out to $z\sim1$. We also find strong evidence for the presence of large-scale structures in the XXL bright cluster sample and identify five new superclusters.