# Validating Planck SZ2 Clusters with Optical Counterparts

## TL;DR

This study cross-matched Planck PSZ2 galaxy clusters with SDSS-based optical catalogs, identifying new counterparts, analyzing redshifts, and exploring the detectability of optical clusters through Planck's y-map, enhancing cluster validation and catalog completeness.

## Contribution

The paper extends the number of optical counterparts for Planck clusters, compares multiple catalogs for redshift consistency, and identifies new cluster candidates not in the PSZ2 catalog.

## Key findings

- 485 (or 511) optical matches found by AMF DR9, including 45 (or 55) new counterparts.
- Good agreement between redMaPPer and AMF DR9 redshift estimates.
- Detection of 20 new cluster candidates using MMF technique in Planck data.

## Abstract

We perform an extensive analysis of optical counterparts of Planck PSZ2 clusters, considering matches with three recent catalogs built from 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 for both optical and X--ray determinations. We then analyze the Planck Cosmology sample and comment on redshift determination and potential mass mis-determinations due to alignment issues. Finally, we inspect the reconstructed $y$ map from Planck and reason on the detectability of optical clusters. Overall, AMF DR9 main (extended) finds 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 followup 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. From the Planck Cosmology sample, we find 14 clusters which merit further investigation, and discuss possible alignment issues for 9 of these clusters. After inspecting the $y$ map, we provide a list of 229 optical clusters not included in the Planck PSZ2 catalog but showing a prominent $y$ signal. We have further investigated the 86 clusters with Planck S/N $>4.5$ using the MMF technique (applied to the Planck HFI maps), and were able to detect 20 new cluster candidates that are not included in the PSZ2 catalog.