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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents



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ID: 559334.0, MPI für Astronomie / Publikationen_mpia
Deep Gemini/GMOS imaging of an extremely isolated globular cluster in the Local Group
Authors:Mackey, A. D.; Ferguson, A. M. N.; Irwin, M. J.; Martin, N. F.; Huxor, A. P.; Tanvir, N. R.; Chapman, S. C.; Ibata, R. A.; Lewis, G. F.; McConnachie, A. W.
Language:English
Date of Publication (YYYY-MM-DD):2010
Title of Journal:Monthly Notices of the Royal Astronomical Society
Journal Abbrev.:MNRAS
Volume:401
Issue / Number:1
Start Page:533
End Page:546
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We report on deep imaging of a remote M31 globular cluster, MGC1, obtained with Gemini/GMOS. Our colour-magnitude diagram for this object extends ~5 mag below the tip of the red-giant branch and exhibits features consistent with an ancient metal-poor stellar population, including a long, well-populated horizontal branch. The red-giant branch locus suggests MGC1 has a metal abundance [M/H] ~ -2.3. We measure the distance to MGC1 and find that it lies ~160 kpc in front of M31 with a distance modulus μ = 23.95 +/- 0.06. Combined with its large projected separation of Rp = 117 kpc from M31, this implies a deprojected radius of Rgc = 200 +/- 20 kpc, rendering it the most isolated known globular cluster in the Local Group by some considerable margin. We construct a radial brightness profile for MGC1 and show that it is both centrally compact and rather luminous, with MV = -9.2. Remarkably, the cluster profile shows no evidence for a tidal limit and we are able to trace it to a radius of at least 450 pc, and possibly as far as ~900 pc. The profile exhibits a power-law fall-off with exponent γ = -2.5, breaking to γ = -3.5 in its outermost parts. This core-halo structure is broadly consistent with expectations derived from numerical models, and suggests that MGC1 has spent many gigayears in isolation.
Free Keywords:globular clusters: general; galaxies: individual: M31
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:URL:http://adsabs.harvard.edu/abs/2010MNRAS.401..533M [ID No:1]
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