A dynamics-free lower bound on the mass of our galaxy

TL;DR

This paper establishes a lower bound on the Milky Way's mass using baryonic and halo gas measurements, challenging recent low-mass estimates and emphasizing the importance of baryon fraction consistency.

Contribution

It introduces a new lower bound on the Milky Way's mass based on baryonic and halo gas data, addressing discrepancies with dynamical estimates.

Findings

Lower bound on MW mass: 7.7×10^11 M_sun

Estimated MW mass likely ≥ 1.2×10^12 M_sun

Rejection of low mass estimates inconsistent with baryon fraction

Abstract

We use a sample of Milky Way (MW) analogs for which we have stellar and disk gas mass measurements, published measurements of halo gas masses of the MW and of similar galaxies, and the well-established value of the cosmological baryon fraction to place a lower bound on the mass of the Galaxy of $7.7\times10^{11} M_\odot$ and estimate that the mass is likely to be $\ge 1.2\times10^{12}$ M$_\odot$. Although most dynamical analyses yield measurements consistent with these results, several recent studies have advocated for a total mass well below $10^{12} M_\odot$. We reject such low mass estimates because they imply a Galactic baryon matter fraction significantly above the universal value. Convergence between dynamical mass estimates and those based on the baryonic mass is an important milestone in our understanding of galaxies.