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