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

We identify new clusters and characterize previously unknown PlanckSunyaev-Zeldovich (SZ) sources from the first Planckcatalogue 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 IsaacNewton telescope, the 3.5m Telescopio Nazionale Galileo, the 4.2m William Herschel telescopeand the 10.4m Gran Telescopio Canarias. We characterize 115 new PSZ1 sources using deep optical imagingand spectroscopy. We adopt robust criteria in order to consolidate the SZ counterparts by analysing the optical richness, the 2D galaxy distribution, and velocity dispersionsof clusters. Confirmed counterparts are considered to be validated if they are rich structures, well aligned with the PlanckPSZ1 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), 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 cirrusin the optical images, mainly in the SZ target located at low galactic latitudes, which supports this hypothesis.