Optical Confirmation and Redshift Estimation of the Planck Cluster
  Candidates overlapping the Pan-STARRS Survey
  We report results of a study of Planck Sunyaev-Zel'dovich effect (SZE)
selected galaxy cluster candidates using the Panoramic Survey Telescope & Rapid
Response System (Pan-STARRS) imaging data. We first examine 150 Planck
confirmed galaxy clusters with spectroscopic redshifts to test our algorithm
for identifying optical counterparts and measuring their redshifts; our
redshifts have a typical accuracy of $\sigma_{z/(1+z)} \sim 0.022$ for this
sample. Using 60 random sky locations, we estimate that our chance of
contamination through a random superposition is ~ 3 per cent. We then examine
an additional 237 Planck galaxy cluster candidates that have no redshift in the
source catalogue. Of these 237 unconfirmed cluster candidates we are able to
confirm 60 galaxy clusters and measure their redshifts. A further 83 candidates
are so heavily contaminated by stars due to their location near the Galactic
plane that we do not attempt to identify counterparts. For the remaining 94
candidates we find no optical counterpart but use the depth of the Pan-STARRS1
data to estimate a redshift lower limit $z_{\text{lim}(10^{15})}$ beyond which
we would not have expected to detect enough galaxies for confirmation. Scaling
from the already published Planck sample, we expect that $\sim$12 of these
unconfirmed candidates may be real clusters.
