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Global Properties of M31’s Stellar Halo from the SPLASH Survey. III. Measuring the Stellar Velocity Dispersion Profile

Gilbert, Karoline M. and Tollerud, Erik J. and Beaton, Rachael L. and Guhathakurta, Puragra and Bullock, James S. and Chiba, Masashi and Kalirai, Jason S. and Kirby, Evan N. and Majewski, Steven R. and Tanaka, Mikito (2018) Global Properties of M31’s Stellar Halo from the SPLASH Survey. III. Measuring the Stellar Velocity Dispersion Profile. Astrophysical Journal, 852 (2). Art. No. 128. ISSN 1538-4357. doi:10.3847/1538-4357/aa9f26.

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We present the velocity dispersion of red giant branch stars in M31's halo, derived by modeling the line-of-sight velocity distribution of over 5000 stars in 50 fields spread throughout M31's stellar halo. The data set was obtained as part of the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) Survey, and covers projected radii of 9 to 175 kpc from M31's center. All major structural components along the line of sight in both the Milky Way (MW) and M31 are incorporated in a Gaussian Mixture Model, including all previously identified M31 tidal debris features in the observed fields. The probability that an individual star is a constituent of M31 or the MW, based on a set of empirical photometric and spectroscopic diagnostics, is included as a prior probability in the mixture model. The velocity dispersion of stars in M31's halo is found to decrease only mildly with projected radius, from 108 km s_(−1) in the innermost radial bin (8.2 to 14.1 kpc) to ~80 to 90 km s^(−1) at projected radii of ~40–130 kpc, and can be parameterized with a power law of slope −0.12 ± 0.05. The quoted uncertainty on the power-law slope reflects only the precision of the method, although other sources of uncertainty we consider contribute negligibly to the overall error budget.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Gilbert, Karoline M.0000-0003-0394-8377
Tollerud, Erik J.0000-0002-9599-310X
Beaton, Rachael L.0000-0002-1691-8217
Guhathakurta, Puragra0000-0001-8867-4234
Bullock, James S.0000-0003-4298-5082
Chiba, Masashi0000-0002-9053-860X
Kalirai, Jason S.0000-0001-9690-4159
Kirby, Evan N.0000-0001-6196-5162
Majewski, Steven R.0000-0003-2025-3147
Additional Information:© 2018 The American Astronomical Society. Received 2017 April 30. Accepted 2017 November 20. Published 2018 January 15. Support for this work was provided by NASA through a Giacconi Fellowship (E.J.T.) and Hubble Fellowship grants 51316.01 and 51386.01 awarded to E.J.T. and R.L.B. by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. K.M.G. and E.N.K. acknowledge support from NSF grants AST-1614569 and AST-1614081. R.L.B. and S.R.M. acknowledge support from NSF grants AST-1413269 and AST-1009882. P.G. and J.S.B. acknowledge support from collaborative NSF grants AST-1412648, AST-1010039, AST-1009973. M.T. and M.C. acknowledge support from Grant-in-Aid for Scientific Research (2580098 for M.T., 16H01086 and 17H01101 for M.C.) of the Ministry of Education, Culture, Sports, Science, and Technology of Japan. The analysis pipeline used to reduce the DEIMOS data was developed at UC Berkeley with support from NSF grant AST-0071048.
Group:SPLASH, COSMOS, Infrared Processing and Analysis Center (IPAC), Astronomy Department
Funding AgencyGrant Number
NASA Giacconi FellowshipUNSPECIFIED
NASA Hubble Fellowship51316.01
NASA Hubble Fellowship51386.01
Ministry of Education, Culture, Sports, Science and Technology (MEXT)2580098
Ministry of Education, Culture, Sports, Science and Technology (MEXT)16H01086
Ministry of Education, Culture, Sports, Science and Technology (MEXT)17H01101
Issue or Number:2
Record Number:CaltechAUTHORS:20180117-095337937
Persistent URL:
Official Citation:Karoline M. Gilbert et al 2018 ApJ 852 128
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84360
Deposited By: Ruth Sustaita
Deposited On:18 Jan 2018 00:11
Last Modified:02 Nov 2021 20:53

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