Phat stellar cluster survey. II. Andromeda project cluster catalog

L. Clifton Johnson, Anil C. Seth, Julianne J. Dalcanton, Matthew L. Wallace, Robert J. Simpson, Chris J. Lintott, Amit Kapadia, Evan D. Skillman, Nelson Caldwell, Morgan Fouesneau, Daniel R. Weisz, Benjamin F. Williams, Lori C. Beerman, Dimitrios A. Gouliermis, Ata Sarajedini

Research output: Contribution to journalArticlepeer-review

63 Scopus citations


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 2753 clusters and 2270 background galaxies within ∼0.5 deg2 of PHAT imaging searched, or ∼400 kpc2 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 M 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 de finitive base data product for PHAT cluster science, providing a census of star clusters in an L∗ spiral galaxy with unmatched sensitivity and quality.

Original languageEnglish (US)
Article number127
JournalAstrophysical Journal
Issue number2
StatePublished - Apr 1 2015

Bibliographical note

Publisher Copyright:
© 2015. The American Astronomical Society. All rights reserved.


  • Catalogs
  • Galaxies: individual (M31)
  • Galaxies: star clusters: general


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