The SLUGGS survey: globular cluster stellar population trends from weak absorption lines in stacked spectra

Usher, Christopher, Forbes, Duncan A., Brodie, Jean P., Romanowsky, Aaron J., Strader, Jay, Conroy, Charlie, Foster, Caroline, Pastorello, Nicola, Pota, Vincenzo and Arnold, Jacob A. 2015, The SLUGGS survey: globular cluster stellar population trends from weak absorption lines in stacked spectra, Monthly notices of the Royal Astronomical Society, vol. 446, no. 1, pp. 369-390, doi: 10.1093/mnras/stu2050.

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Title The SLUGGS survey: globular cluster stellar population trends from weak absorption lines in stacked spectra
Author(s) Usher, Christopher
Forbes, Duncan A.
Brodie, Jean P.
Romanowsky, Aaron J.
Strader, Jay
Conroy, Charlie
Foster, Caroline
Pastorello, NicolaORCID iD for Pastorello, Nicola
Pota, Vincenzo
Arnold, Jacob A.
Journal name Monthly notices of the Royal Astronomical Society
Volume number 446
Issue number 1
Start page 369
End page 390
Total pages 22
Publisher Oxford University Press
Place of publication London, Eng.
Publication date 2015-01
ISSN 0035-8711
Keyword(s) globular clusters
general – galaxies
abundances – galaxies
star clusters
stellar content
Summary As part of the SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) survey, we stack 1137 Keck DEIMOS (Deep Imaging Multi-Object Spectrograph) spectra of globular clusters from 10 galaxies to study their stellar populations in detail. The stacked spectra have median signal-to-noise ratios of ~90 Å -1 . Besides the calcium triplet, we study weaker sodium, magnesium, titanium and iron lines as well as the Hα and higher order Paschen hydrogen lines. In general, the stacked spectra are consistent with old ages and a Milky Way-like initial mass function. However, we see different metal line index strengths at fixed colour and magnitude, and differences in the calcium triplet-colour relation from galaxy to galaxy. We interpret this as strong evidence for variations in the globular cluster colour-metallicity relation between galaxies. Two possible explanations for the colour-metallicity relation variations are that the average ages of globular clusters vary from galaxy to galaxy or that the average abundances of light elements (i.e. He, C, N and O) differ between galaxies. Stacking spectra by magnitude, we see that the colours become redder and metal line indices stronger with brighter magnitudes. These trends are consistent with the previously reported 'blue tilts' being mass-metallicity relations.
Language eng
DOI 10.1093/mnras/stu2050
Field of Research 0201 Astronomical And Space Sciences
HERDC Research category C1.1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Copyright notice ©2014, The Authors
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