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New Constraints on Early-type Galaxy Assembly from Spectroscopic Metallicities of Globular Clusters in M87
The Astrophysical Journal (2019)
  • Alexa Villaume, University of California, Santa Cruz
  • Aaron J. Romanowsky, San Jose State University
  • Jean Brodie, University of California, Santa Cruz
  • Jay Strader, Michigan State University
The observed characteristics of globular cluster (GC) systems, such as metallicity distributions, are commonly used to place constraints on galaxy formation models. However, obtaining reliable metallicity values is particularly difficult because of our limited means to obtain high quality spectroscopy of extragalactic GCs. Often, "color–metallicity relations" are invoked to convert easier-to-obtain photometric measurements into metallicities, but there is no consensus on what form these relations should take. In this paper we make use of multiple photometric data sets and iron metallicity values derived from applying full-spectrum stellar population synthesis models to deep Keck/LRIS spectra of 177 GCs centrally located around M87 to obtain a new color–metallicity relation. Our new relation differs substantially from previous relations in the blue, and we present evidence that the M87 relation differs from that of the Milky Way GCs, suggesting environmental dependence of GC properties. We use our color–metallicity relation to derive a new GC metallicity-host galaxy luminosity relation for red and blue GCs and find a shallower relation for the blue GCs than what previous work has found and that the metal-poor GCs are more enriched than what was previously found. This could indicate that the progenitor satellite galaxies that now make up the stellar halos of early-type galaxies are more massive and formed later than previously thought, or that the properties of metal-poor GCs are less dependent on their present-day host, indicating a common origin.
  • galaxies: evolution,
  • galaxies: individual (M87),
  • galaxies: star clusters: general
Publication Date
July 3, 2019
Publisher Statement
This article was published in The Astrophysical Journal, volume 879, issue 1, 2019 and can also be found at this link. Copyright © 2019, American Astronomical Society. All rights reserved.

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Citation Information
Alexa Villaume, Aaron J. Romanowsky, Jean Brodie and Jay Strader. "New Constraints on Early-type Galaxy Assembly from Spectroscopic Metallicities of Globular Clusters in M87" The Astrophysical Journal Vol. 879 Iss. 1 (2019) ISSN: 0004637X
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