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Unmixing the Galactic Halo with RR Lyrae tagging.

Belokurov, V. and Deason, A. J. and Koposov, S. E. and Catelan, M. and Erkal, D. and Drake, A. J. and Evans, N. W. (2018) 'Unmixing the Galactic Halo with RR Lyrae tagging.', Monthly notices of the Royal Astronomical Society., 477 (2). pp. 1472-1483.


We show that tagging RR Lyrae stars according to their location in the period-amplitude diagram can be used to shed light on the genesis of the Galactic stellar halo. The mixture of RR Lyrae of ab type, separated into classes along the lines suggested by Oosterhoff, displays a strong and coherent evolution with Galactocentric radius. The change in the RR Lyrae composition appears to coincide with the break in the halo’s radial density profile at ∼25 kpc. Using simple models of the stellar halo, we establish that at least three different types of accretion events are necessary to explain the observed RRab behavior. Given that there exists a correlation between the RRab class fraction and the total stellar content of a dwarf satellite, we hypothesize that the field halo RRab composition is controlled by the mass of the progenitor contributing the bulk of the stellar debris at the given radius. This idea is tested against a suite of cosmological zoom-in simulations of Milky Way-like stellar halo formation. Finally, we study some of the most prominent stellar streams in the Milky Way halo and demonstrate that their RRab class fractions follow the trends established previously.

Item Type:Article
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Publisher statement:This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record Belokurov, Belokurov, V., Deason, A. J., Koposov, S. E., Catelan, M., Erkal, D., Drake, A. J. & Evans, N. W. (2018). Unmixing the Galactic Halo with RR Lyrae tagging. Monthly Notices of the Royal Astronomical Society 477(2): 1472-1483 is available online at:
Date accepted:27 February 2018
Date deposited:06 April 2018
Date of first online publication:08 March 2018
Date first made open access:No date available

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