ACS Photometry of Newly Discovered Globular Clusters in the Outer Halo of M31

We report the first results from deep ACS imaging of 10 classical globular clusters in the far outer regions (15 kpc R sub(p) 100 kpc) of M31. Eight of the clusters, including two of the most remote M31 globular clusters presently known, are described for the first time. Our F606W, F814W color-magni...

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Vydáno v:The Astrophysical journal Ročník 655; číslo 2; s. L85 - L88
Hlavní autoři: Mackey, A. D, Huxor, A, Ferguson, A. M. N, Tanvir, N. R, Irwin, M, Ibata, R, Bridges, T, Johnson, R. A, Lewis, G
Médium: Journal Article
Jazyk:angličtina
Vydáno: Chicago, IL IOP Publishing 01.02.2007
University of Chicago Press
Témata:
Astronomy
Earth, ocean, space
Exact sciences and technology
Galaxy halo
Globular clusters
galaxies: halos-galaxies: individual (M31)-globular clusters: general
Photometry
ISSN:1538-4357, 0004-637X, 1538-4357
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Shrnutí:We report the first results from deep ACS imaging of 10 classical globular clusters in the far outer regions (15 kpc R sub(p) 100 kpc) of M31. Eight of the clusters, including two of the most remote M31 globular clusters presently known, are described for the first time. Our F606W, F814W color-magnitude diagrams extend 6 3 mag below the horizontal branch and clearly demonstrate that the majority of these objects are old ( 10 Gyr), metal-poor clusters. Five have [Fe/H] 6 -2.1, while an additional four have -1.9 [Fe/H] -1.5. The remaining object is more metal-rich, with [Fe/H] 6 -0.70. Several clusters exhibit the second-parameter effect. Using aperture photometry, we estimate integrated luminosities and structural parameters for all clusters. Many, including all four clusters with projected radii greater than 45 kpc, are compact and very luminous, with -8.9 M sub(V) -8.3. These four outermost clusters are thus quite unlike their Milky Way counterparts, which are typically diffuse, subluminous (-6.0 M sub(V) -4.7), and more metal-rich (-1.8 [Fe/H] -1.3).
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ISSN:1538-4357
0004-637X
1538-4357
DOI:10.1086/511977