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arXiv · 1607.08628

The age structure of the Milky Way's halo

D. Carollo·T. C. Beers·V. M. Placco·R. M. Santucci·P. Denissenkov·P. B. Tissera·G. Lentner·S. Rossi·Y. S. Lee·J. Tumlinson
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Abstract

We present a new, high-resolution chronographic (age) map of the Milky Way's halo, based on the inferred ages of ~130,000 field blue horizontal-branch (BHB) stars with photometry from the Sloan Digital Sky Survey. Our map exhibits a strong central concentration of BHB stars with ages greater than 12 Gyr, extending up to ~15 kpc from the Galactic center (reaching close to the solar vicinity), and a decrease in the mean ages of field stars with distance by 1-1.5 Gyr out to ~45-50 kpc, along with an apparent increase of the dispersion of stellar ages, and numerous known (and previously unknown) resolved over-densities and debris streams, including the Sagittarius Stream. These results agree with expectations from modern LambdaCDM cosmological simulations, and support the existence of a dual (inner/outer) halo system, punctuated by the presence of over-densities and debris streams that have not yet completely phase-space mixed.

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D. Carollo, T. C. Beers, V. M. Placco, R. M. Santucci, P. Denissenkov, P. B. Tissera, G. Lentner, S. Rossi, Y. S. Lee, J. Tumlinson. 2016-09-07. The age structure of the Milky Way's halo. https://doi.org/10.1038/nphys3874

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