Validating Planck SZ2 clusters with optical counterparts

Abstract We perform an extensive analysis of optical counterparts of Planck PSZ2 clusters, considering matches with three recent catalogs built from Sloan Digital Sky Survey (SDSS) data: AMF DR9, redMaPPer (v6.3) and Wen et al (WHL). We significantly extend the number of optical counterparts of detected Planck clusters, and characterize the optical properties when multiple identifications in different catalogs exist. For Planck clusters which already possess an external validation, we analyze the redshift assignment from both optical and X–ray observations. We then analyze the Planck Cosmology Sample and comment on redshift and potential mass mis-determinations due to alignment issues. Finally, we inspect the reconstructed y-map from Planck and comment on the possibility of detecting further optical clusters. Overall, using the AMF DR9 main (extended) catalog, we find 485 (511) optical matches, with 45 (55) previously unmatched PSZ2 clusters, to be compared with the 374 optical matches already present in PSZ2. 29 of the 55 previously unmatched clusters do not yet have a follow-up observation in the literature. 18 of these are found in more than one SDSS catalog with consistent redshifts. We provide redshift and mass estimates for the newly matched clusters, and discuss the comparison with the follow-ups, when present. We find good agreement between the redMaPPer and AMF DR9 redshift determinations. AMF DR9 tends to predict lower redshifts for a few PSZ2 high–redshift clusters which were previously validated by an optical counterpart. From the Planck Cosmology Sample, optical matches are found for 204 of the 278 objects in the observed area. We find 14 clusters which merit further investigation and discuss possible alignment issues for 9 of them. After inspecting the y-map, we provide a list of 229 optical clusters not included in the Planck PSZ2 catalog, yet showing a prominent y signal. We have further investigated the clusters with the most prominent y signal using a proper MMF technique and we find 20 (12) clusters with a S/N  >  4.5 ( >  6) which are not included in the PSZ2 (cosmology sample) catalog. We discuss point source contamination for these objects.