Spiral Arm Crossings in Gaia: A Non-Equilibrium Determination of the Local Density

by Eric David Kramer

Hebrew University
at Particles and Fields Seminar

Mon, 20 Jan 2020, 14:00
Sacta-Rashi Building for Physics (54), room 207


The advent of the Gaia mission has given us to the chance to know our Galaxy on a much more personal level. Large scale features, as well as snail shell patterns in the velocity distributions teach us that our Milky Way disk is far from being in perfect equilibrium. These non-equilibrium features become of particular interest when trying to determine the Galactic potential. Indeed, Jeans analyses rely on the assumption that the star populations studied are in equilibrium with the Galactic potential. It has been noted by several authors that non-equilibrium features could bias these determinations to incorrectly imply a smaller Milky Way disk mass. In this paper, we ask a different question: can the non-equilibrium features themselves be used to measure the Galactic potential? Here, we show that indeed, the Gaia data contain breathing modes, presumably the result of recent spiral arm passages, whose wavelength, combined with spiral arm data, provide an independent measurement of the oscillation period and by extension the Galactic potential. In contrast to Jeans analyses, the results require a significant dark disk component.

Created on 13-01-2020 by Kats, Yevgeny (katsye)
Updaded on 19-01-2020 by Kats, Yevgeny (katsye)