Dynamically constraining the length of the Milky way bar
Abstract
We present a novel method for constraining the length of the Galactic bar using 6D phasespace information to directly integrate orbits. We define a pseudolength for the Galactic bar, named R_{Freq}, based on the maximal extent of trapped bar orbits. We find the R_{Freq} measured from orbits is consistent with the R_{Freq} of the assumed potential only when the length of the bar and pattern speed of said potential is similar to the model from which the initial phasespace coordinates of the orbits are derived. Therefore, one can measure the model's or the Milky Way's bar length from 6D phasespace coordinates by determining which assumed potential leads to a selfconsistent measured R_{Freq}. When we apply this method to ≈210 000 stars in APOGEE DR17 and Gaia eDR3 data, we find a consistent result only for potential models with a dynamical bar length of ≈3.5 kpc. We find the Milky Way's trapped bar orbits extend out to only ≈3.5 kpc, but there is also an overdensity of stars at the end of the bar out to 4.8 kpc which could be related to an attached spiral arm. We also find that the measured orbital structure of the bar is strongly dependent on the properties of the assumed potential.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2023
 DOI:
 10.1093/mnras/stad406
 arXiv:
 arXiv:2206.01798
 Bibcode:
 2023MNRAS.520.4779L
 Keywords:

 Galaxy: bulge;
 Galaxy: evolution;
 Galaxy: kinematics and dynamics;
 Galaxy: structure;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 15 pages, 8 figures, 2 tables, accepted to MNRAS, comments welcome