A Lower Limit on the Mass of Our Galaxy from the H3 Survey

Abstract

The timing argument provides a lower limit on the mass of the Milky Way. We find, using a sample of 32 stars at $R>60$ kpc drawn from the H3 Spectroscopic Survey and mock catalogs created from published numerical simulations, that M${}_{200}>0.91\times 10^{12}$ M${}_{\odot }$ with 90% confidence. We recommend using this limit to refine the allowed prior mass range in more complex and sophisticated statistical treatments of Milky Way dynamics. The use of such a prior would have significantly reduced many previously published uncertainty ranges. Our analysis suggests that the most likely value of M${}_{200}$ is $\sim 1.4\times 10^{12}$ M${}_{\odot }$, but establishing this as the Milky Way mass requires a larger sample of outer halo stars and a more complete analysis of the inner halo stars in H3. The imminent growth in the sample of outer halo stars due to ongoing and planned surveys will make this possible.

8 pages, submitted for publication