How to quench a dwarf galaxy: The impact of inhomogeneous reionization on dwarf galaxies and cosmic filaments

 We use the SPHINX suite of high-resolution cosmological radiation hydrodynamics simulations to study how spatially and temporally inhomogeneous reionization impacts the baryonic content of dwarf galaxies and cosmic filaments. 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 per cent following reionization. The gas inflow rates into haloes with ${M_{\rm vir}\lesssim 10^8\, \mathrm{M}_{\odot }}$ 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 halo masses ${M_{\rm vir}\lesssim 7\times 10^7\, \mathrm{M}_{\odot }}$. 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 galaxies is regulated. At fixed redshift and halo mass, there is a large scatter in the halo baryon fractions that is entirely dictated by the timing of reionization in the local region surrounding a halo which can change by Δz ≳ 3 at fixed mass. Finally, although the gas content of high-redshift dwarf galaxies is significantly impacted by reionization, we find that most haloes with ${M_{\rm vir}\lesssim 10^8\, \mathrm{M}_{\odot }}$ can remain self-shielded and form stars long after reionization, until their local gas reservoir is depleted, suggesting that Local Group dwarf galaxies do not necessarily exhibit star formation histories that peak prior to z = 6. Significantly larger simulation boxes will be required to capture the full process of reionization and understand how our results translate to environments not probed by our current work.