Emily C. Cunningham
HALO7D II: The Halo Velocity Ellipsoid and Velocity Anisotropy with Distant Main-sequence Stars
Cunningham, Emily C.; Deason, Alis J.; Sanderson, Robyn E.; Sohn, Sangmo Tony; Anderson, Jay; Guhathakurta, Puragra; Rockosi, Constance M.; van der Marel, Roeland P.; Loebman, Sarah R.; Wetzel, Andrew
Authors
Professor Alis Deason alis.j.deason@durham.ac.uk
Professor
Robyn E. Sanderson
Sangmo Tony Sohn
Jay Anderson
Puragra Guhathakurta
Constance M. Rockosi
Roeland P. van der Marel
Sarah R. Loebman
Andrew Wetzel
Abstract
The Halo Assembly in Lambda Cold Dark Matter: 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, the second in the HALO7D series, we present the proper motions for the HALO7D sample. We discuss our measurement methodology, which makes use of a Bayesian mixture modeling approach for creating the stationary reference frame of distant galaxies. Using the 3D kinematic HALO7D sample, we estimate the parameters of the halo velocity ellipsoid, ávfñ, sr, sf, sq, and the velocity anisotropy β. Using the full HALO7D sample, we find b = - 0.68+0.05 0.04 at árñ = 23 kpc. We also estimate the ellipsoid parameters for our sample split into three apparent magnitude bins; the posterior medians for these estimates of β are consistent with one another. Finally, we estimate β in each of the individual HALO7D fields. We find that the velocity anisotropy β can vary from field-to field, which suggests that the halo is not phase-mixed at árñ = 23 kpc. We explore the β variation across the skies of two stellar halos from the Latte suite of FIRE-2 simulations, finding that both simulated galaxies show β variation over a range similar to that of the variation observed across the four HALO7D fields. The accretion histories of the two simulated galaxies result in different β variation patterns; spatially mapping β is thus a way forward in characterizing the accretion history of the Galaxy.
Citation
Cunningham, E. C., Deason, A. J., Sanderson, R. E., Sohn, S. T., Anderson, J., Guhathakurta, P., Rockosi, C. M., van der Marel, R. P., Loebman, S. R., & Wetzel, A. (2019). HALO7D II: The Halo Velocity Ellipsoid and Velocity Anisotropy with Distant Main-sequence Stars. Astrophysical Journal, 879(2), Article 120. https://doi.org/10.3847/1538-4357/ab24cd
Journal Article Type | Article |
---|---|
Acceptance Date | May 24, 2019 |
Online Publication Date | Jul 15, 2019 |
Publication Date | Jul 10, 2019 |
Deposit Date | Aug 2, 2019 |
Publicly Available Date | Aug 2, 2019 |
Journal | Astrophysical Journal |
Print ISSN | 0004-637X |
Publisher | American Astronomical Society |
Peer Reviewed | Peer Reviewed |
Volume | 879 |
Issue | 2 |
Article Number | 120 |
DOI | https://doi.org/10.3847/1538-4357/ab24cd |
Public URL | https://durham-repository.worktribe.com/output/1296085 |
Files
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Copyright Statement
© 2019. The American Astronomical Society. All rights reserved.
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