The Impact of Local Stellar Radiation on Dwarf Galaxy Formation around Milky Way Analogs across Cosmic Reionization

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Abstract We explore the effect of local stellar radiation on the formation and evolution of dwarf galaxies around Milky Way (MW) analogs. Using five simulations from the Auriga project, both with and without local stellar radiation, we find that local stellar radiation, as a pre-reionization source, is highly effective at photoionizing and heating the gas around the proto-MW analogs. As a result, the formation of surrounding dwarf galaxies in dark matter halos with masses below approximately 109.5 M ⊙ is significantly suppressed. After reionization, the intensity of local stellar radiation eventually becomes comparable to the ultraviolet background. Consequently, the impact of local stellar radiation on the surrounding dwarf galaxy formation decreases with decreasing redshift and nearly vanishes after redshift z = 4. At present day, the bright satellite population in the simulations with and without local stellar radiation is nearly identical. While our simulations do not have sufficient resolution to resolve the faintest satellite galaxies that are most prone to the local stellar radiation, we use the accreted galaxy mass function to assess the impact and find that the reduction in the faintest satellite is around 13% in the presence of local stellar radiation, but this difference is within ∼2σ of the Poisson uncertainty and thus not statistically significant.