Apocenter Pile-up: Origin of the Stellar Halo Density Break

Deason, Alis J.; Belokurov, Vasily; Koposov, Sergey E.; Lancaster, Lachlan

doi:10.3847/2041-8213/aad0ee

Apocenter Pile-up: Origin of the Stellar Halo Density Break

Deason, Alis J.; Belokurov, Vasily; Koposov, Sergey E.; Lancaster, Lachlan

Authors

Dr Alis Deason alis.j.deason@durham.ac.uk
Associate Professor

Vasily Belokurov

Sergey E. Koposov

Lachlan Lancaster

Abstract

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.

Citation

Deason, A. J., Belokurov, V., Koposov, S. E., & Lancaster, L. (2018). Apocenter Pile-up: Origin of the Stellar Halo Density Break. Astrophysical Journal Letters, 862(1), Article L1. https://doi.org/10.3847/2041-8213/aad0ee

Journal Article Type	Article
Acceptance Date	Jul 3, 2018
Online Publication Date	Jul 16, 2018
Publication Date	Jul 16, 2018
Deposit Date	Aug 2, 2018
Publicly Available Date	Aug 2, 2018
Journal	Astrophysical Journal Letters
Print ISSN	2041-8205
Publisher	American Astronomical Society
Peer Reviewed	Peer Reviewed
Volume	862
Issue	1
Article Number	L1
DOI	https://doi.org/10.3847/2041-8213/aad0ee