ACS Photometry of Extended, Luminous Globular Clusters in the Outskirts of M31

A. D. Mackey, A. Huxor, A. M. N. Ferguson, N. R. Tanvir, M. Irwin, R. Ibata, T. Bridges, R. A. Johnson, G. Lewis

Research output: Contribution to journalArticlepeer-review

Abstract

A new population of extended, luminous globular clusters has recently been discovered in the outskirts of M31. These objects have luminosities typical of classical globular clusters, but much larger half-light radii. We report the first results from deep ACS imaging of four such clusters, one of which is a newly discovered example lying at a projected distance of ~60 kpc from M31. Our F606W, F814W color-magnitude diagrams extend ~3 mag below the horizontal branch level, and clearly demonstrate, for the first time, that all four clusters are composed of >~10 Gyr old, metal-poor stellar populations. No evidence for multiple populations is observed. From a comparison with Galactic globular cluster fiducials we estimate metallicities in the range -2.2
Original languageEnglish
JournalAstrophysical Journal
Volume653
Issue number2
DOIs
Publication statusPublished - 1 Dec 2006

Keywords

  • Galaxies: Individual: Messier Number: M31
  • Galaxies: Star Clusters
  • Galaxy: Globular Clusters: General

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