Dwarf galaxies in voids: suppressing star formation with photoheating 论文

摘要

We study structure formation in cosmological void regions using high-resolution hydrodynamical simulations. Despite being significantly underdense, voids are populated abundantly with small dark matter halos which should appear as dwarf galaxies if their star formation is not suppressed significantly. We here investigate to which extent the cosmological UV-background reduces the baryon content of dwarf galaxies, and thereby limits their cooling and star formation rates. Assuming a Haardt & Madau UVbackground with reionisation at redshift z = 6, our samples of simulated galaxies show that halos with masses below a characteristic mass of Mc(z = 0) = 6.5 × 10 9 h −1 M⊙ are baryon-poor, but in general not completely empty, because baryons that are in the condensed cold phase or are already locked up in stars resist evaporation. In halos with mass M � Mc, we find that photo-heating suppresses further cooling of gas. The redshift and UV-background dependent characteristic mass Mc(z) can be understood from the equilibrium temperature between heating and cooling at a characteristic overdensity of δ ≃ 1000. If a halo is massive enough to compress gas to this density