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HALO7D I. The Line-of-sight Velocities of Distant Main-sequence Stars in the Milky Way Halo

Cunningham, Emily C.; Deason, Alis J.; Rockosi, Constance M.; Guhathakurta, Puragra; Jennings, Zachary G.; Kirby, Evan N.; Toloba, Elisa; Barro, Guillermo

HALO7D I. The Line-of-sight Velocities of Distant Main-sequence Stars in the Milky Way Halo Thumbnail


Emily C. Cunningham

Constance M. Rockosi

Puragra Guhathakurta

Zachary G. Jennings

Evan N. Kirby

Elisa Toloba

Guillermo Barro


The Halo Assembly in Lambda-CDM: Observations in 7 Dimensions (HALO7D) data set consists of Keck II/DEIMOS spectroscopy and Hubble Space Telescope–measured proper motions of Milky Way halo main-sequence turnoff stars in the CANDELS fields. In this paper, we present the spectroscopic component of this data set and discuss target selection, observing strategy, and survey properties. We present a new method of measuring line-of-sight (LOS) velocities by combining multiple spectroscopic observations of a given star, utilizing Bayesian hierarchical modeling. We present the LOS velocity distributions of the four HALO7D fields and estimate their means and dispersions. All of the LOS distributions are dominated by the "hot halo": none of our fields are dominated by substructure that is kinematically cold in the LOS velocity component. Our estimates of the LOS velocity dispersions are consistent across the different fields, and these estimates are consistent with studies using other types of tracers. To complement our observations, we perform mock HALO7D surveys using the synthetic survey software Galaxia to "observe" the Bullock & Johnston accreted stellar halos. Based on these simulated data sets, the consistent LOS velocity distributions across the four HALO7D fields indicate that the HALO7D sample is dominated by stars from the same massive (or few relatively massive) accretion event(s).

Journal Article Type Article
Acceptance Date Apr 4, 2019
Online Publication Date Apr 10, 2019
Publication Date May 10, 2019
Deposit Date May 29, 2019
Publicly Available Date May 30, 2019
Journal Astrophysical Journal
Print ISSN 0004-637X
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 876
Issue 2
Article Number 124
Public URL


Published Journal Article (36 Mb)

Copyright Statement
© 2019. The American Astronomical Society. All rights reserved.

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