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25 April 2024 |
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Quantifying Kinematic Substructure in the Milky Way's Stellar Halo | | Xiang-Xiang Xue
; Hans-Walter Rix
; Brian Yanny
; Timothy C. Beers
; Eric F. Bell
; Gang Zhao
; James S. Bullock
; Kathryn V. Johnston
; Heather Morrison
; Constance Rockosi
; Sergey E. Koposov
; Xi Kang
; Chao Liu
; Ali Luo
; Young Sun Lee
; Benjamin. A. Weaver
; | | Date: |
8 Nov 2010 | | Abstract: | We present and analyze the positions, distances, and radial velocities for
over 4000 blue horizontal-branch (BHB) stars in the Milky Way’s halo, drawn
from SDSS DR8. We search for position-velocity substructure in these data,
which is expected from hierarchical galaxy formation models, where most of the
halo stars are still-detectable tidal debris from disrupted satellite galaxies.
Using a cumulative "close pair distribution" (CPD) as a statistic in the
4-dimensional space of sky position, distance, and velocity, we quantify the
presence of position-velocity substructure at high statistical significance
among the BHB stars: pairs of BHB stars that are close in position on the sky
tend to have more similar distances and radial velocities compared to a random
sampling of these overall distributions. We make analogous mock-observations of
11 numerical halo formation simulations, in which the stellar halo is entirely
composed of disrupted satellites debris, and find a level of substructure
comparable to that seen in the actually observed BHB star sample. This result
quantitatively confirms the hierarchical build-up of the stellar halo through a
signature in phase (position-velocity) space. In detail, the structure present
in the BHB stars is somewhat less prominent than that seen in most simulated
halos, quite possibly because BHB stars represent an older sub-population. BHB
stars located in the outer halo, beyond 10 kpc from the Galactic center,
exhibit statistically stronger substructure signatures than at $
m r_{gc} <
10$ kpc. | | Source: | arXiv, 1011.1925 | | Services: | Forum | Review | PDF | Favorites | |
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