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Constraining the length and pattern speed of the Milky Way bar from direct orbit integration

Presentation #400.01 in the session Galactic Bars.

Published onApr 25, 2022
Constraining the length and pattern speed of the Milky Way bar from direct orbit integration

The dynamics of the inner Galaxy contain crucial clues for untangling the evolutionary history of the Milky Way. However, the gravitational potential of the inner Galaxy is poorly constrained, partly because the precise structure of the Galactic bar is unknown. Specifically, the length of the Galactic bar is currently under debate with length estimates ranging from 3.5-5 kpc. Here, I present a novel method for constraining the length and pattern speed of the Galactic bar using the 6D phase space information of ~210,000 stars from Gaia/APOGEE to directly integrate orbits of Milky Way bar stars. First, I use N-body simulations to validate the method, and then I apply it to APOGEE DR17 and Gaia eDR3 data. I find that the orbit-derived bar length is self-consistent with the potential’s bar length only when the structure of the gravitational potential is similar to the N-body model from which the initial positions and velocities of the stars are taken. When I apply the method to the observed data, I expect to find a self-consistent bar length only for a potential that is representative of the APOGEE and Gaia data, i.e., the actual Galactic bar mass distribution. With my method, I can test a variety of potential models and determine which potentials best fit the observed data for the Galactic bar. In this talk, I will present new constraints on the length and pattern speed of the Galactic bar and the potential of the inner Galaxy.


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