First Gaia Dynamics of the Andromeda System: DR2 Proper Motions, Orbits, and Rotation of M31 and M33
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Author
van der Marel, Roeland P.
Fardal, Mark A.
Sohn, Sangmo Tony

Patel, Ekta
Besla, Gurtina
Pino, Andrés del
Sahlmann, Johannes
Watkins, Laura L.

Affiliation
Univ Arizona, Dept AstronIssue Date
2019-02-10
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IOP PUBLISHING LTDCitation
Roeland P. van der Marel et al 2019 ApJ 872 24Journal
ASTROPHYSICAL JOURNALRights
© 2019. The American Astronomical Society. All rights reserved.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
The 3D velocities of M31 and M33 are important for understanding the evolution and cosmological context of the Local Group. Their most massive stars are detected by Gaia, and we use Data Release 2 (DR2) to determine the galaxy proper motions (PMs). We select galaxy members based on, e.g., parallax, PM, color-magnitude diagram location, and local stellar density. The PM rotation of both galaxies is confidently detected, consistent with the known line-of-sight rotation curves: V-rot = -206 +/- 86 km s(-1) (counterclockwise) for M31, and V-rot = 80 +/- 52 km s(-1) (clockwise) for M33. We measure the center-of-mass PM of each galaxy relative to surrounding background quasars in DR2. This yields that (mu(alpha*), mu(delta)) equals (65 +/- 18, -57 +/- 15) mu as yr(-1) for M31 and (31 +/- 19, -29 +/- 16) mu as yr(-1) for M33. In addition to the listed random errors, each component has an additional residual systematic error of 16 mu as yr(-1). These results are consistent at 0.8 sigma and 1.0 sigma with the (2 and 3 times higher accuracy) measurements already available from Hubble Space Telescope (HST) optical imaging and Very Long Baseline Array water maser observations, respectively. This lends confidence that all these measurements are robust. The new results imply that the M31 orbit toward the Milky Way (MW) is somewhat less radial than previously inferred, V-tan,V-DR2 +/- HST = 57(-31)(+35) km s(-1), and strengthen arguments that M33 may be on its first infall into M31. The results highlight the future potential of Gaia for PM studies beyond the MW satellite system.ISSN
1538-4357Version
Final published versionAdditional Links
http://stacks.iop.org/0004-637X/872/i=1/a=24?key=crossref.77eed68e5832879642e2a6b74dae2ee2ae974a485f413a2113503eed53cd6c53
10.3847/1538-4357/ab001b