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Title

Hubble space telescope ACS wide-field photometry of the Sombrero galaxy globular cluster system

Author(s)

Spitler, Lee R.;  Larsen, Soren S.;  Strader, Jay;  Brodie, Jean P.;  Forbes, Duncan A.;  Beasley, Michael A.

Abstract

A detailed imaging analysis of the globular cluster (GC) system of the Sombrero galaxy (NGC 4594) has been accomplished using a six-image mosaic from the Hubble Space Telescope Advanced Camera for Surveys. The quality of the data is such that contamination by foreground stars and background galaxies is negligible for all but the faintest 5% of the GC luminosity function. This enables the study of an effectively pure sample of 659 GCs until ~2 mag fainter than the turnover magnitude, which occurs at MVTOM = -7.60 ± 0.06 for an assumed m - M = 29.77. Two GC metallicity subpopulations are easily distinguishable, with the metal-poor subpopulation exhibiting a smaller intrinsic dispersion in color compared to the metal-rich subpopulation. There are three new discoveries. (1) A metal-poor GC color-magnitude trend has been observed. (2) The fact that the metal-rich GCs are ~17% smaller than the metal-poor ones for small projected galactocentric radii (less than ~2') has been confirmed. However, the median half-light radii of the two subpopulations become identical at ~3' from the center. This is most easily explained if the size difference is the result of projection effects. (3) The brightest (MV < -9.0) members of the GC system show a size-magnitude upturn, where the average GC size increases with increasing luminosity. Evidence is presented that supports an intrinsic origin for this feature rather than being a result of accreted dwarf elliptical nuclei. In addition, the metal-rich GCs show a shallower positive size-magnitude trend, similar to what is found in previous studies of young star clusters.

Publication type

Journal article

Research centre

Swinburne University of Technology. Faculty of Information and Communication Technologies. Centre for Astrophysics and Supercomputing

Source

Astronomical Journal, Vol. 132, no. 4 (2006), p. 1593-1609

Publication year

2006

Keyword(s)

Galaxies;  M104;  NGC 4594;  Spiral galaxies;  Galaxy star clusters

Publisher

University of Chicago Press

ISSN

0004-6256

Publisher URL

http://dx.doi.org/10.1086/507328

Copyright

Copyright © 2006 The American Astronomical Society. Reproduced in accordance with the copyright policy of the publisher.

Full text

Peer reviewed