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

Cunningham, Emily C. and Deason, Alis J. and Rockosi, Constance M. and Guhathakurta, Puragra and Jennings, Zachary G. and Kirby, Evan N. and Toloba, Elisa and Barro, Guillermo (2019) HALO7D I. The Line-of-sight Velocities of Distant Main-sequence Stars in the Milky Way Halo. Astrophysical Journal, 876 (2). Art. No. 124. ISSN 1538-4357.

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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).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Cunningham, Emily C.0000-0002-6993-0826
Deason, Alis J.0000-0001-6146-2645
Guhathakurta, Puragra0000-0001-8867-4234
Kirby, Evan N.0000-0001-6196-5162
Toloba, Elisa0000-0001-6443-5570
Barro, Guillermo0000-0001-6813-875X
Additional Information:© 2019. The American Astronomical Society. Received 2018 September 3; revised 2019 March 19; accepted 2019 April 4; published 2019 May 10. Over the course of this work, E.C. was supported by a National Science Foundation Graduate Research Fellowship and an ARCs Foundation Fellowship, as well as NSF grant AST-1616540. Partial support for this work was provided by NASA through grants for program AR-13272 from the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. E.C. expresses her profound gratitude to Alexander Rudy, a conversation with whom sparked the radial velocity measurement technique outlined in this work. E.C. also thanks Tony Sohn for his help with Figure 1. A.D. is supported by a Royal Society University Research Fellowship. A.D. also acknowledges support from the STFC grant ST/P000451/1. P.G. and E.T. acknowledge support from the NSF grants AST-1010039 and AST-1412504. We thank the outstanding team at Keck Observatory for assisting us in our observations. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013, 2018). This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Universidad Complutense de Madrid (UCM), partnered with the University of California Observatories at Santa Cruz (UCO/Lick, UCSC). We recognize and acknowledge the significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Group:Astronomy Department
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
Science and Technology Facilities Council (STFC)ST/P000451/1
Subject Keywords:Galaxy: halo; Galaxy: kinematics and dynamics; methods: statistical; techniques: radial velocities
Issue or Number:2
Record Number:CaltechAUTHORS:20190510-105529766
Persistent URL:
Official Citation:Emily C. Cunningham et al 2019 ApJ 876 124
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95395
Deposited By: George Porter
Deposited On:10 May 2019 20:27
Last Modified:03 Oct 2019 21:13

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