The M33 globular cluster system with PAndAS data: The last outer halo cluster?

Robert Cockcroft*, William E. Harris, Annette M.N. Ferguson, Avon Huxor, Rodrigo Ibata, Mike J. Irwin, Alan W. McConnachie, Kristin A. Woodley, Scott C. Chapman, Geraint F. Lewis, Thomas H. Puzia

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

27 Citations (Scopus)


We use CFHT/MegaCam data to search for outer halo star clusters in M33 as part of the Pan-Andromeda Archaeological Survey. This work extends previous studies out to a projected radius of 50kpc and covers over 40deg2. We find only one new unambiguous star cluster in addition to the five previously known in the M33 outer halo (10kpc ≤ r ≤ 50kpc). Although we identify 2440 cluster candidates of various degrees of confidence from our objective image search procedure, almost all of these are likely background contaminants, mostly faint unresolved galaxies. We measure the luminosity, color, and structural parameters of the new cluster in addition to the five previously known outer halo clusters. At a projected radius of 22kpc, the new cluster is slightly smaller, fainter, and redder than all but one of the other outer halo clusters, and has g′ 19.9, (g′ - i′) 0.6, concentration parameter c 1.0, a core radius rc 3.5 pc, and a half-light radius rh 5.5 pc. For M33 to have so few outer halo clusters compared to M31 suggests either tidal stripping of M33's outer halo clusters by M31, or a very different, much calmer accretion history of M33.

Original languageEnglish
Article number112
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 1 Apr 2011


  • galaxies: evolution
  • galaxies: halos
  • galaxies: individual (M33)
  • galaxies: spiral
  • galaxies: star clusters: general
  • Local Group


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