Abstract
The outer halo regions of early-type galaxies carry key information about their past accretion history. However, spectroscopically probing the stellar component at such galactocentric radii is still challenging. Using the DEep Imaging Multi-Object Spectrograph on the Keck, we have been able to measure the metallicities of the stellar and globular cluster components in 12 early-type galaxies out to more than 10Re. We find similar metallicity gradients for the metal-poor and metal-rich globular cluster subpopulations, suggesting a common formation process for the two subpopulations. This is in conflict with most current theoretical predictions, where the metal-poor globular clusters are thought to be purely accreted and metal-rich globular clusters mostly formed in situ. Moreover, we find that the globular cluster metallicity gradients show a trend with galaxy mass, being steeper in lower mass galaxies than in higher mass galaxies. This is similar to what we find for the outermost galaxy stars and suggests a more active accretion history, with a larger role played by major mergers, in the most massive galaxies. This conclusion is qualitatively consistent with expectations from two-phase galaxy assembly models. Finally, we find that the small difference in metallicity between galaxy stars and metal-rich globular clusters at 1Re may correlate with galaxy mass. The origin of this difference is not currently clear.
Original language | English |
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Pages (from-to) | 2625-2639 |
Number of pages | 15 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 451 |
Issue number | 3 |
DOIs | |
Publication status | Published - 11 Aug 2015 |
Bibliographical note
Copyright 2015 The Authors. First published in Monthly notices of the Royal Astronomical Society, 451(3), 2625-2639. The original publication is available at http://doi.org/10.1093/mnras/stv1131, published by Oxford University Press on behalf of the Royal Astronomical Society. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.Keywords
- galaxies: abundances
- galaxies: elliptical and lenticular, cD
- galaxies: evolution
- galaxies: formation
- galaxies: star clusters: general
- galaxies: stellar content