The Quenched Fraction of Satellites around Simulated Milky Way–Mass Galaxies

Abstract We compare satellite quenched fractions across three cosmological simulation suites (FIREbox, the FIRE-2 zoom-ins, and IllustrisTNG50) and observational datasets from Satellites Around Galactic Analogs (SAGA), ELVES, and the combined satellite population of the Milky Way (MW) and M31. To enable consistent comparisons, we select MW-mass hosts with M halo = 10 11.9 –10 12.2 M ⊙ and satellites with stellar masses of 10 7 –10 10 M ⊙ , applying nearly uniform radial selections and a common quenching definition. All three simulations reproduce the strong observed trend that lower-mass satellites are more likely to be quenched, closely matching the stellar mass dependence seen in SAGA, ELVES, and the MW and M31 system. This agreement indicates that the mass dependence of satellite quenching is a robust outcome of contemporary galaxy formation models. Radial trends, however, show greater diversity. SAGA and ELVES exhibit gently declining quenched fractions with projected distance, consistent with stronger quenching at small radii. TNG50 most closely matches this behavior, while FIREbox remains broadly consistent with a weak radial trend within uncertainties. The FIRE-2 zoom-ins show suppressed quenched fractions at small projected distances, driven primarily by their paired MW–M31 analogs. We show that this discrepancy is not explained by host environment alone, but instead reflects atypical satellite populations in the paired systems, where star-forming and quenched satellites occupy distinct spatial distributions. Overall, our results demonstrate that stellar-mass-quenched fraction trends are robust across simulations and observations, while radial trends are more sensitive to the detailed properties and distributions of satellite populations.