The SAGA Survey V

We compare theoretical predictions to SAGA satellite stellar mass functions, quenched fractions, spatial distributions, and star formation rates, along with SDSS isolated galaxy quenched fractions. These data enable the first systematic constraints on the faint-end galaxy–halo connection across environments.

UniverseMachine is an empirical model that predicts galaxy star formation histories based on dark matter halo assembly. We construct a new version, UM-SAGA, to model low-mass galaxy populations. UM-SAGA uses dark matter halo assembly histories from cosmological simulations and does not assume satellite-specific quenching mechanisms.

Nearly all isolated dwarf galaxies are star-forming while a significant fraction of low-mass satellites are quenched. For the first time, UM-SAGA accurately captures this dichotomy across the stellar mass range probed by SAGA.

The spatial distributions of quenched and star-forming satellites critically constrain galaxy quenching physics. UM-SAGA matches the radial distribution of both quenched and star-forming SAGA satellites.

When do low-mass galaxies form their stars? Our new model predicts significantly earlier dwarf galaxy star formation histories due to the inclusion of SAGA data, similar to the reconstructed star formation histories of low-mass galaxies in the Local Group.

UM-SAGA predicts galaxy quenching based on halo assembly alone. The different quenched fractions of SAGA satellites and isolated dwarf galaxies result in a strong correlation between halo assembly and star formation in our model, which can be tested by future dwarf galaxy surveys.