Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 442, Issue 2, Pages 1003-1039Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stu937
Keywords
galaxies: abundances; galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: formation; galaxies: stellar content
Categories
Funding
- W. M. Keck Foundation
- NSF [AST-0071048, AST-1109878, AST-0909237]
- ARC [DP130100388]
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [1109878] Funding Source: National Science Foundation
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Stellar metallicity gradients in the outer regions of galaxies are a critical tool for disentangling the contributions of in situ and ex situ formed stars. In the two-phase galaxy formation scenario, the initial gas collapse creates steep metallicity gradients, while the accretion of stars formed in satellites tends to flatten these gradients in the outskirts, particularly for massive galaxies. This work presents the first compilation of extended metallicity profiles over a wide range of galaxy mass. We use the DEep Imaging Multi-Object Spectrograph spectrograph on the Keck telescope in multislit mode to obtain radial stellar metallicity profiles for 22 nearby early-type galaxies. From the calcium triplet lines in the near-infrared, we measure the metallicity of the starlight up to 3 effective radii. We find a relation between the outer metallicity gradient and galaxy mass, in the sense that lower mass systems show steeper metallicity gradients than more massive galaxies. This result is consistent with a picture in which the ratio of ex situ to in situ formed stars is lower in less massive galaxies as a consequence of the smaller contribution by accretion. In addition, we infer a correlation between the strength of the calcium triplet feature in the near-infrared and the stellar initial mass function slope that is consistent with recent models in the literature.
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