Optical validation and characterization of Planck PSZ2 sources at the Canary Islands observatories. II. Second year of LP15 observations

TL;DR

This paper reports on the second year of optical follow-up observations to validate Planck PSZ2 galaxy cluster sources, improving the sample's purity and analyzing false detection causes related to galactic dust emission.

Contribution

It provides the final results of the LP15 follow-up program, enhancing the validation process and understanding of PSZ2 source reliability.

Findings

Purity of PSZ2 increased from 76.7% to 86.2%.

Confirmed galaxy clusters using velocity dispersion and richness criteria.

False detections correlate with galactic thermal dust emission.

Abstract

We present the second and last year of observations of our optical follow-up programme 128-MULTIPLE-16/15B (LP15 )at Roque de los Muchachos Observatory (La Palma), which has been developed with the aim of validating all the unidentified PSZ2 sources in the northern sky, with declination above -15deg, and with no correspondence in the first Planck catalogue PSZ1. We adopt a robust confirmation criteria based on velocity dispersion and richness estimations in order to carry out the final classification of the new galaxy clusters as the optical counterparts of the PSZ2 detections. We also present final results of the programme, showing an update of the purity and completeness of the PSZ2 sample. After the LP15 programme, we find that the purity of the PSZ2 has increased from 76.7% originally to 86.2%. In addition, we study the possible reasons of having false detection, and we report a clear correlation between the number of unconfirmed sources and galactic thermal dust emission.