Optical validation and characterization of Planck PSZ1 sources at the Canary Islands observatories. I. First year of ITP13 observations

TL;DR

This study validates and characterizes 115 Planck SZ sources using optical observations from Canary Islands telescopes, confirming 53 clusters and analyzing contamination effects near the galactic plane.

Contribution

First optical validation and characterization of PSZ1 SZ sources using multi-telescope observations, establishing criteria for confirming cluster counterparts.

Findings

Confirmed 53 new galaxy clusters from PSZ1 sources.

Approximately 46% of the studied SZ sources were validated.

Higher contamination near the galactic plane due to galactic cirrus.

Abstract

We identify new clusters and characterize previously unknown Planck Sunyaev-Zeldovich (SZ) sources from the first Planck catalogue of SZ sources (PSZ1). The results presented here correspond to an optical follow-up observational programme developed during approximately one year (2014) at Roque de los Muchachos Observatory, using the 2.5m Isaac Newton telescope, the 3.5m Telescopio Nazionale Galileo, the 4.2m William Herschel telescope and the 10.4m Gran Telescopio Canarias. We characterize 115 new PSZ1 sources using deep optical imaging and spectroscopy. We adopt robust criteria in order to consolidate the SZ counterparts by analysing the optical richness, the 2D galaxy distribution, and velocity dispersions of clusters. Confirmed counterparts are considered to be validated if they are rich structures, well aligned with the Planck PSZ1 coordinate and show relatively high velocity dispersion. Following this classification, we confirm 53 clusters, which means that 46% of this PSZ1 subsample has been validated and characterized with this technique. Sixty-two SZ sources (54% of this PSZ1 subset) remain unconfirmed. In addition, we find that the fraction of unconfirmed clusters close to the galactic plane (at |b|<25deg) is greater than that at higher galactic latitudes (|b|>25deg), which indicates contamination produced by radio emission of galactic dust and gas clouds on these SZ detections. In fact, in the majority of the cases, we detect important galactic cirrus in the optical images, mainly in the SZ target located at low galactic latitudes, which supports this hypothesis.