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Apocenter pile-up : origin of the stellar halo density break.

Deason, Alis J. and Belokurov, Vasily and Koposov, Sergey E. and Lancaster, Lachlan (2018) 'Apocenter pile-up : origin of the stellar halo density break.', Astrophysical journal letters., 862 (1). L1.


We measure the orbital properties of halo stars using seven-dimensional information provided by Gaia and the Sloan Digital Sky Survey. A metal-rich population of stars, present in both local main sequence stars and more distant blue horizontal branch stars, have very radial orbits (eccentricity ~0.9) and apocenters that coincide with the stellar halo "break radius" at galactocentric distance r ~ 20 kpc. Previous work has shown that the stellar halo density falls off much more rapidly beyond this break radius. We argue that the correspondence between the apocenters of high metallicity, high-eccentricity stars, and the broken density profile is caused by the build-up of stars at the apocenter of a common dwarf progenitor. Although the radially biased stars are likely present down to metallicities of [Fe/H] ~ −2, the increasing dominance at higher metallicities suggests a massive dwarf progenitor, which is at least as massive as the Fornax and Sagittarius dwarf galaxies, and is likely the dominant progenitor of the inner stellar halo.

Item Type:Article
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Publisher statement:© 2018. The American Astronomical Society. All rights reserved.
Date accepted:03 July 2018
Date deposited:02 August 2018
Date of first online publication:16 July 2018
Date first made open access:02 August 2018

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