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

Research output: Contribution to journalArticlepeer-review

30 Citations (Scopus)


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 Centre (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 lambda cold dark matter 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.

Original languageEnglish
Pages (from-to)1170-1176
Number of pages7
JournalNature Physics
Issue number12
Publication statusPublished - 1 Dec 2016

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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