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Durham University

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Publication details for Dr Alis Deason

Deason, Alis J., Belokurov, Vasily, Koposov, Sergey E. & Lancaster, Lachlan (2018). Apocenter Pile-up: Origin of the Stellar Halo Density Break. The Astrophysical Journal Letters 862(1): L1.

Author(s) from Durham


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.