Planck 2015 results. XXVII. The second Planck catalogue of Sunyaev-Zeldovich sources

We present the all-sky Planck catalogue of Sunyaev-Zeldovich (SZ) sources detected from the 29 month full-mission data. The catalogue (PSZ2) is the largest SZ-selected sample of galaxy clusters yet produced and the deepest systematic all-sky surveyof galaxy clusters. It contains 1653 detections, of which 1203 are confirmed clusters with identified counterparts in external data sets, and is the first SZ-selected cluster survey containing >103 confirmed clusters. We present a detailed analysis of the survey selection function in terms of its completeness and statistical reliability, placing a lower limit of 83% on the purity. Using simulations, we find that the estimates of the SZ strength parameter Y5R500are robust to pressure-profile variation and beam systematics, but accurate conversion to Y500 requires the use of prior information on the cluster extent. We describe the multi-wavelength search for counterparts in ancillary data, which makes use of radio, microwave, infra-red, optical, and X-ray data sets, and which places emphasis on the robustness of the counterpart match. We discuss the physical properties of the new sample and identify a population of low-redshift X-ray under-luminous clusters revealed by SZ selection. These objects appear in optical and SZ surveys with consistent properties for their mass, but are almost absent from ROSAT X-ray selected samples

Evolution of clusters and cosmology

International audienceRecent Sunyaev–Zeldovich (SZ) surveys (ACT, Planck, SPT) have provided new cluster catalogs, very significantly expanding the coverage of the mass–redshift plane, while XMM-Newton surveys are pushing cluster detection to lower masses, up to z ∼ 1 and beyond. Cosmological analysis of the new cluster samples, particularly that of the largest Planck sample, found fewer clusters than predicted by the base Planck ΛCDM model derived from cosmic microwave (CMB) anisotropies. This could imply a need for extension of the model and/or a revision of cluster physics. In parallel, Chandra and XMM-Newton follow-up programs on these new SZ-discovered clusters have improved our knowledge of evolution, as well as providing new information on survey selection. These results challenge our understanding of fundamental issues such as (a) what the true mass of clusters is, with implications for the baryon depletion at cluster scales and cluster dynamical evolution, and (b) what the true underlying population is, that we are only partly detecting at various wavelengths. Potential new observations to address these issues with XMM-Newton in conjunction with other observatories are discussed