Journal Article

Halo globular clusters observed with AAOmega: dark matter content, metallicity and tidal heating

Richard R. Lane, László L. Kiss, Geraint F. Lewis, Rodrigo A. Ibata, Arnaud Siebert, Timothy R. Bedding, Péter Székely, Zoltán Balog and Gyula M. Szabó

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 4, pages 2732-2742
Published in print August 2010 | ISSN: 0035-8711
Published online August 2010 | e-ISSN: 1365-2966 | DOI:
Halo globular clusters observed with AAOmega: dark matter content, metallicity and tidal heating

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Globular clusters (GCs) have proven to be essential to our understanding of many important astrophysical phenomena. Here, we analyse spectroscopic observations of 10 halo GCs to determine their dark matter (DM) content, their tidal heating by the Galactic disc and halo, describe their metallicities and the likelihood that Newtonian dynamics explains their kinematics. We analyse a large number of members in all clusters, allowing us to address all these issues together, and we have included NGC 288 and M30 to overlap with previous studies. We find that any flattening of the velocity dispersion profiles in the outer regions of our clusters can be explained by tidal heating. We also find that all our GCs have M/LV≲ 5, therefore, we infer the observed dynamics do not require DM, or a modification of gravity. We suggest that the lack of tidal heating signatures in distant clusters indicates the halo is not triaxial. The isothermal rotations of each cluster are measured, with M4 and NGC 288 exhibiting rotation at a level of 0.9 ± 0.1 km s−1 and 0.25 ± 0.15 km s−1, respectively. We also indirectly measure the tidal radius of NGC 6752, determining a more realistic figure for this cluster than current literature values. Lastly, an unresolved and intriguing puzzle is uncovered with regard to the cooling of the outer regions of all ten clusters.

Keywords: gravitation; stellar dynamics; globular clusters: individual

Journal Article.  6339 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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