An extended star cluster at the outer edge of the spiral galaxy M33

Abstract

We report a discovery of an extended globular-like star cluster, M33-EC1, at the outer edge of the spiral galaxy M33. The distance to the cluster is 890 kpc, and it lies at a 12.5 kpc projected distance from the center of M33. Old age (>~7 Gyr) and low metallicity ([M/H] <~ -1.4) are estimated on the basis of isochrone fits. Color-magnitude diagrams of stars, located in the cluster's area, photometric and structural parameters of the cluster are presented. Cluster's luminosity (M_V = -6.6) and half-light radius (r_h = 20.3 pc) are comparable to those of the extended globular clusters, discovered in more luminous Local Group galaxies, the Milky Way and M31. Extended globular clusters are suspected to be remnants of accreted dwarf galaxies, and the finding of such a cluster in the late-type dwarf spiral galaxy M33 would imply a complex merging history in the past.

20 pages, 6 figures, 2 tables, accepted for publication in AJ

References in corpus (7)

• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
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• Discovery of a Faint Old Stellar System at 150 kpc
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Cited by in corpus (5)

• Scl-dE1 GC1: An Extended Globular Cluster in a Low-Luminosity Dwarf Elliptical Galaxy
• HI clouds in the proximity of M33
• Luminosity-Diameter Relations for Globular Clusters and Dwarf Spheroidal Galaxies
• Ages of M33 Star Clusters Based on the HST/WFPC2 Photometry
• Photometric Survey for Stellar Clusters in the Outer Part of M33