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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.
|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.|
|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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|MNRAS-2010-Mackey-533-46.pdf||Published (publisher PDF)||7.53 MB||Adobe PDF||View/Open|
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