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The SLUGGS survey: inferring the formation epochs of metal-poor and metal-rich globular clusters
Monthly Notices of the Royal Astronomical Society (2015)
  • Duncan A. Forbes, Swinburne University of Technology
  • Nicola Pastorello, Swinburne University of Technology
  • Aaron J. Romanowsky, San Jose State University
  • Christopher Usher, Swinburne University of Technology
  • Jean P. Brodie, University of California Observatories
  • Jay Strader, Michigan State University
We present a novel, observationally-based framework for the formation epochs and sites of globular clusters (GCs) in a cosmological context. Measuring directly the mean ages of the metal-poor and metal-rich GC subpopulations in our own Galaxy, and in other galaxies, is observationally challenging. Here we apply an alternative approach utilizing the property that the galaxy mass–metallicity relation is a strong function of redshift (or look-back age) but is relatively insensitive to galaxy mass for massive galaxies. Assuming that GCs follow galaxy mass–metallicity relations that evolve with redshift, one can estimate the mean formation epochs of the two GC subpopulations by knowing their mean metallicities and the growth in host galaxy mass with redshift. Recently, the SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) survey has measured the spectroscopic metallicities for over 1000 GCs in a dozen massive early-type galaxies. Here we use these measurements, and our new metallicity matching method, to infer a mean age for metal-rich GCs of 11.5 Gyr (z = 2.9) and a range of 12.2–12.8 Gyr (4.8 < z < 5.9) for the metal-poor GCs, depending on whether they mostly formed in accreted satellites or in situ within the main host galaxy. We compare our values to direct age measurements for Milky Way GCs and predictions from cosmological models. Our findings suggest that reionization preceded most GC formation, and that it is unlikely to be the cause of GC bimodal metallicity distributions.
  • galaxies: evolution,
  • galaxies: star clusters: general
Publication Date
September, 2015
Publisher Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
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Citation Information
Duncan A. Forbes, Nicola Pastorello, Aaron J. Romanowsky, Christopher Usher, et al.. "The SLUGGS survey: inferring the formation epochs of metal-poor and metal-rich globular clusters" Monthly Notices of the Royal Astronomical Society Vol. 452 Iss. 1 (2015) p. 1045 - 1051 ISSN: 1365-2966
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