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Paper: The Relative Ages and Fractions of the Accreted and In Situ Populations in the Galactic Halo
Volume: 507, Multi-Object Spectroscopy in the Next Decade: Big Questions, Large Surveys, and Wide Fields
Page: 59
Authors: Hawkins, K.; Jofré, P.; Masseron, T.
Abstract: The inner Galactic halo is thought to be formed by a combination of stars formed in situ and in dwarf galaxies that were accreted onto the Milky Way at later times. The two populations have been shown to be chemically distinct primarily in the α-elements such that the accreted population has lower [α/Fe] compared to the in situ stars at a constant metallicity. In this paper, we outline a powerful new spectral-indexing method to measure the [α/Fe] from low-resolution Sloan Digital Sky Survey spectra, and use the method in addition to turnoff temperature to study the relative age difference between, and age-metallicity relation of, the accreted and in situ populations. Our results indicate that at high metallicities the α-poor population is systematically younger than the α-rich population, but becomes coeval at low metallicities. Finally, we discuss the implication of this finding and potential applications for the new method.
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