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Title: 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.
Chapman, S. C.
Martin, N. F.
Huxor, A. P.
Tanvir, N. R.
Ibata, R. A.
Lewis, G. F.
McConnachie, A. W.
First Published: 1-Jan-2010
Publisher: Oxford University Press (OUP)
Citation: Monthly Notices of the Royal Astronomical Society, 2010, 401 (1), pp. 533-546
Abstract: 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.
DOI Link: 10.1111/j.1365-2966.2009.15678.x
ISSN: 0035-8711
eISSN: 1365-2966
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2010 the authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Deposited with reference to the publisher’s archiving policy available on the SHERPA/RoMEO website.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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