2026 Theses Doctoral

Gas Content, Ram Pressure Stripping, and Star Formation in Low-Mass Satellite Galaxies

Zhu, Jingyao

The smallest "dwarf" galaxies (M_star <= 10^9 M_sun) in low-density environments often have more interstellar gas -- the fuel for star formation -- than stars. But among the dwarf satellite galaxies of the Milky Way and M31, only a few retain gas while dozens more are gas-poor, indicating that the host environment removes satellite gas and ultimately quenches their star formation. This dissertation studies whether the Milky Way/M31 environment is representative of satellite quenching, and how such host environments shape the gas content and star formation of dwarf galaxies, by combining radio observations with hydrodynamical simulations.

We cross-match 21-cm H I data from the ALFALFA, WALLABY, and MHONGOOSE surveys with deep optical data from the DESI Legacy Surveys to compile a sample of 127 gaseous dwarf galaxies around 56 Milky Way-mass or smaller hosts in the local volume. We find that the abundance of gaseous satellites is low, with 0--2 per isolated dwarf host and 0--5 per Milky Way-like spiral host. These abundances are consistent with the Milky Way, M31, and the star-forming satellite abundances from recent deep optical surveys, suggesting that environmental gas loss is common in satellite dwarfs. The gaseous satellites share similar distributions of gas masses (M_HI), H I linewidths, and stellar masses (M_star) with their Local Group counterparts, but are mildly gas-depleted, with lower M_HI/M_star ratios than dwarf galaxies in low-density environments.

We conduct three suites of high-resolution hydrodynamical wind tunnel simulations to investigate quenching by ram pressure stripping (RPS), the direct removal of satellite gas by host halo gas, together with star formation and feedback. We find that early stages of RPS can easily remove the diffuse, circumgalactic gas reservoir in low-mass satellites, preventing future inflows. The typical ram pressure strengths from a single orbit within a smooth Milky Way gaseous halo can rapidly quench low-mass satellites with M_star <= 10⁷ M_sun (or M_200 <= 10¹⁰ M_sun), but are insufficient above this scale. This transitional mass is 0.5-1 dex lower than that found in observations, suggesting that additional mechanisms are needed to quench more massive satellites, such as tidal stripping of the satellite dark matter or RPS from a clumpy gaseous halo. We also find that partial stripping of the dense gas can moderately enhance satellite star formation within the stripping radius, which is caused not directly by compression, but by RPS-driven radial inflows funneling gas into the central regions. We use these simulations to calibrate analytical RPS theories, and find that the dark matter restoring force must be included to accurately predict stripping in low-mass galaxies.