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

We use a sample of Milky Way (MW) analogues for which we have stellar and disc 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 × 10¹¹ M_⊙ and estimate that the mass is likely to be ≥1.2 × 10¹² M_⊙. Although most dynamical analyses yield measurements consistent with these results, several recent studies have advocated for a total mass well below 10¹² M_⊙. 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.