PHAT Stellar Cluster Survey. II. Andromeda Project Cluster Catalog
  We construct a stellar cluster catalog for the Panchromatic Hubble Andromeda
Treasury (PHAT) survey using image classifications collected from the Andromeda
Project citizen science website. We identify 2,753 clusters and 2,270
background galaxies within ~0.5 deg$^2$ of PHAT imaging searched, or ~400
kpc$^2$ in deprojected area at the distance of the Andromeda galaxy (M31).
These identifications result from 1.82 million classifications of ~20,000
individual images (totaling ~7 gigapixels) by tens of thousands of volunteers.
We show that our crowd-sourced approach, which collects >80 classifications per
image, provides a robust, repeatable method of cluster identification. The high
spatial resolution Hubble Space Telescope images resolve individual stars in
each cluster and are instrumental in the factor of ~6 increase in the number of
clusters known within the survey footprint. We measure integrated photometry in
six filter passbands, ranging from the near-UV to the near-IR. PHAT clusters
span a range of ~8 magnitudes in F475W (g-band) luminosity, equivalent to ~4
decades in cluster mass. We perform catalog completeness analysis using >3000
synthetic cluster simulations to determine robust detection limits and
demonstrate that the catalog is 50% complete down to ~500 solar masses for ages
<100 Myr. We include catalogs of clusters, background galaxies, remaining
unselected candidates, and synthetic cluster simulations, making all
information publicly available to the community. The catalog published here
serves as the definitive base data product for PHAT cluster science, providing
a census of star clusters in an L$^*$ spiral galaxy with unmatched sensitivity
and quality.
