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  The Implications of Local Fluctuations in the Galactic Midplane for Dynamical Analysis in the Gaia Era

Beane, A., Sanderson, R. E., Ness, M. K., Johnston, K. V., Grion Filho, D., Mac Low, M.-M., et al. (2019). The Implications of Local Fluctuations in the Galactic Midplane for Dynamical Analysis in the Gaia Era. The Astrophysical Journal, 883.

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 Creators:
Beane, Angus1, Author
Sanderson, Robyn E.1, Author
Ness, Melissa K.1, Author
Johnston, Kathryn V.1, Author
Grion Filho, Douglas1, Author
Mac Low, Mordecai-Mark1, Author
Anglés-Alcázar, Daniel1, Author
Hogg, David W.1, Author
Laporte, Chervin F. P.1, Author
Affiliations:
1Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners, ou_2421692              

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Free keywords: Milky Way disk Milky Way dynamics Milky Way evolution Galaxy structure Orbits Stellar dynamics
 Abstract: Orbital properties of stars, computed from their six-dimensional phase- space measurements and an assumed Galactic potential, are used to understand the structure and evolution of the Galaxy. Stellar actions, computed from orbits, have the attractive quality of being invariant under certain assumptions and are therefore used as quantitative labels of a star’s orbit. We report a subtle but important systematic error that is induced in the actions as a consequence of local midplane variations expected for the Milky Way. This error is difficult to model because it is non-Gaussian and bimodal, with neither mode peaking on the null value. An offset in the vertical position of the Galactic midplane of ∼15 pc for a thin disk-like orbit or ∼120 pc for a thick disk-like orbit induces a 25% systematic error in the vertical action J z . In Feedback in Realistic Environments simulations of Milky Way- mass galaxies, these variations are on the order of ∼100 pc at the solar circle. From observations of the mean vertical velocity variation of ∼5─10 km s−1 with radius, we estimate that the Milky Way midplane variations are ∼60─170 pc, consistent with three-dimensional dust maps. Action calculations and orbit integrations, which assume the global and local midplanes are identical, are likely to include this induced error, depending on the volume considered. Variation in the local standard of rest or distance to the Galactic center causes similar issues. The variation of the midplane must be taken into account when performing dynamical analysis across the large regions of the disk accessible to Gaia and future missions.

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 Dates: 2019
 Publication Status: Published in print
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Title: The Astrophysical Journal
Source Genre: Journal
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Pages: - Volume / Issue: 883 Sequence Number: - Start / End Page: - Identifier: -