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The Outer Halo of the Milky Way as Probed by RR Lyr Variables from the Palomar Transient Facility

Cohen, Judith G. and Sesar, Branimir and Bahnolzer, Sophianna and He, Kevin and Kulkarni, Shrinivas R. and Prince, Thomas A. and Bellm, Eric and Laher, Russ R. (2017) The Outer Halo of the Milky Way as Probed by RR Lyr Variables from the Palomar Transient Facility. Astrophysical Journal, 849 (2). Art. No. 150. ISSN 1538-4357. https://resolver.caltech.edu/CaltechAUTHORS:20171113-103138961

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Abstract

RR Lyrae stars are ideal massless tracers that can be used to study the total mass and dark matter content of the outer halo of the Milky Way (MW). This is because they are easy to find in the light-curve databases of large stellar surveys and their distances can be determined with only knowledge of the light curve. We present here a sample of 112 RR Lyr stars beyond 50 kpc in the outer halo of the MW, excluding the Sgr streams, for which we have obtained moderate-resolution spectra with Deimos on the Keck II Telescope. Four of these have distances exceeding 100 kpc. These were selected from a much larger set of 447 candidate RR Lyr stars that were data-mined using machine-learning techniques applied to the light curves of variable stars in the Palomar Transient Facility database. The observed radial velocities taken at the phase of the variable corresponding to the time of observation were converted to systemic radial velocities in the Galactic standard of rest. From our sample of 112 RR Lyr stars we determine the radial velocity dispersion in the outer halo of the MW to be ~90 km s^(−1) at 50 kpc, falling to about 65 km s^(−1) near 100 kpc once a small number of major outliers are removed. With reasonable estimates of the completeness of our sample of 447 candidates and assuming a spherical halo, we find that the stellar density in the outer halo declines as r^(-4).


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/aa9120DOIArticle
http://iopscience.iop.org/article/10.3847/1538-4357/aa9120/metaPublisherArticle
https://arxiv.org/abs/1710.01276arXivDiscussion Paper
ORCID:
AuthorORCID
Cohen, Judith G.0000-0002-8039-4673
Sesar, Branimir0000-0002-0834-3978
He, Kevin0000-0001-5806-0370
Kulkarni, Shrinivas R.0000-0001-5390-8563
Prince, Thomas A.0000-0002-8850-3627
Bellm, Eric0000-0001-8018-5348
Laher, Russ R.0000-0003-2451-5482
Additional Information:© 2017 The American Astronomical Society. Received 2017 April 26; revised 2017 September 26; accepted 2017 September 28; published 2017 November 9. Based in part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. We are grateful to the many people who have worked to make the Keck Telescope and its instruments a reality and to operate and maintain the Keck Observatory. The authors wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented herein would have been possible. We thank the referee for helpful detailed comments that improved this paper. This work uses data obtained with the 1.2 m Samuel Oschin Telescope at Palomar Observatory as part of the Palomar Transient Factory project, a scientific collaboration among the California Institute of Technology, Columbia University, Las Cumbres Observatory, the Lawrence Berkeley National Laboratory, the National Energy Research Scientific Computing Center, the University of Oxford, and the Weizmann Institute of Science; and the Intermediate Palomar Transient Factory project, a scientific collaboration among the California Institute of Technology, Los Alamos National Laboratory, the University of Wisconsin, Milwaukee, the Oskar Klein Center, the Weizmann Institute of Science, the TANGO Program of the University System of Taiwan, and the Kavli Institute for the Physics and Mathematics of the Universe. The Intermediate Palomar Transient Factory project is a scientific collaboration among the California Institute of Technology, Los Alamos National Laboratory, the University of Wisconsin, Milwaukee, the Oskar Klein Center, the Weizmann Institute of Science, the TANGO Program of the University System of Taiwan, and the Kavli Institute for the Physics and Mathematics of the Universe. The PTF database (DR3) is now publicly available at https://www.ptf.caltech.edu/news/DR3. It includes photometry through 2015 January 28. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III website is http://www.sdss3.org/. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration, including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. J.G.C. and B.S. acknowledge NSF grant AST-0908139 to J.G.C. for partial support during the initial early stages of this project. S.R.B. and K.H. thank the Caltech Summer Undergraduate Research Fellowship (SURF) program for support.
Group:Infrared Processing and Analysis Center (IPAC), Palomar Transient Factory, Astronomy Department
Funders:
Funding AgencyGrant Number
Alfred P. Sloan FoundationUNSPECIFIED
Participating InstitutionsUNSPECIFIED
NSFUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
NASA/JPL/CaltechUNSPECIFIED
NSFAST-0908139
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Subject Keywords:Galaxy: halo – Galaxy: kinematics and dynamics – stars: variables: RR Lyrae
Issue or Number:2
Record Number:CaltechAUTHORS:20171113-103138961
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20171113-103138961
Official Citation:Judith G. Cohen et al 2017 ApJ 849 150
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83147
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:14 Nov 2017 03:40
Last Modified:09 Mar 2020 13:18

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