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. Using a sample of 32 stars at R  > 60 kpc drawn from the H3 Spectroscopic Survey and mock catalogs created from published numerical simulations, we find that M 200  > 0.91 × 10 12 M ⊙ 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 ≈1.5 × 10 12 M ⊙ , 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.