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Title: The structure of star clusters in the outer halo of M31
Authors: Tanvir, N. R.
Mackey, A. D.
Ferguson, A. M. N.
Huxor, A.
Read, J. I.
Lewis, G. F.
Irwin, M. J.
Chapman, S.
Ibata, R.
Wilkinson, M. I.
McConnachie, A. W.
Martin, N. F.
Davies, M. B.
Bridges, T. J.
First Published: 1-May-2012
Citation: Monthly Notices of the Royal Astronomical Society , 2012, 422 (1), pp. 162-184
Abstract: We present a structural analysis of halo star clusters in M31 based on deep Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging. The clusters in our sample span a range in galactocentric projected distance from 13 to 100 kpc and thus reside in rather remote environments. Ten of the clusters are classical globulars, whilst four are from the Huxor et al. population of extended, old clusters. For most clusters, contamination by M31 halo stars is slight, and so the profiles can be mapped reliably to large radial distances from their centres. We find that the extended clusters are well fit by analytic King profiles with ∼20 parsec core radii and ∼100 parsec photometric tidal radii, or by Sérsic profiles of index ∼1 (i.e. approximately exponential). Most of the classical globulars also have large photometric tidal radii in the range 50–100 parsec; however, the King profile is a less good fit in some cases, particularly at small radii. We find 60 per cent of the classical globular clusters exhibit cuspy cores which are reasonably well described by Sérsic profiles of index ∼2–6. Our analysis also reinforces the finding that luminous classical globulars, with half-light radii <10 parsec, are present out to radii of at least 100 kpc in M31, which is in contrast to the situation in the Milky Way where such clusters (other than the unusual object NGC 2419) are absent beyond 40 kpc.
DOI Link: 10.1111/j.1365-2966.2012.20590.x
ISSN: 0035-8711
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 ©: 2012 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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