How to Quench a Dwarf Galaxy: The Impact of Inhomogeneous Reionization on Dwarf Galaxies and Cosmic Filaments.

We use the SPHINXsuite of high-resolution cosmological radiation hydrodynamics simulations to study how spatially and temporally inhomogeneous reionizationimpacts the baryonic content of dwarf galaxiesand cosmic filaments. The SPHINXsimulations simultaneously capture the large-scale process of reionization, model the escape of ionising radiation from thousands of galaxies, and resolve haloeswell below the atomic cooling threshold. This makes them an ideal tool for examining how reionizationimpacts star formation and the gas content of dwarf galaxies. We compare simulations with and without stellar radiation to isolate the effects of radiation feedback from that of supernova, cosmic expansion, and numerical resolution. We find that the gas content of cosmic filaments can be reduced by more than 80% following reionization. The gas inflow rates into haloeswith $M_{vir}\lesssim10^8M_{\odot}$ are strongly affected and are reduced by more than an order of magnitude compared to the simulation without reionization. A significant increase in gas outflow rates is found for halomasses $M_{vir}\lesssim7\times10^7M_{\odot}$. Our simulations show that inflow suppression (i.e. starvation), rather than photoevaporation, is the dominant mechanism by which the baryonic content of high-redshift dwarf galaxiesis regulated. At fixed redshift and halomass, there is a large scatter in the halobaryon fractions that is entirely dictated by the timing of reionizationin the local region surrounding a halo. Finally, although the gas content of high-redshift dwarf galaxiesis significantly impacted by reionization, we find that most haloeswith $M_{vir}\lesssim10^8M_{\odot}$ can remain self-shielded and form stars long after reionization, until their local gas reservoir is depleted, suggesting that local group dwarf galaxiesdo not necessarily exhibit star formation histories that peak prior to $z=6$.