Feedback effects on population III star formation

With the help of numerical simulations, we examine two aspects of feedback from the first generation of stars on later star formation. First, we investigate the impact of relic HII regions on forming halos. We find that the positive and negative effects of such feedback nearly cancel because the increase in entropy due to heating is balanced by the increase in the H 2 fraction due to the free electrons. However, these halos can be delayed more easily by a background Lyman-Werner flux. Second, we show that HD cooling is important in halos which have been ionized and allowed to recombine. Gas is allowed to cool to the CMB temperature at densities around n∼10 4cm-3, reducing the accreted mass by a factor of a few. However, as the collapse proceeds, the central gas density exceeds the critical density of HD and heats until HD cooling is no longer important. Therefore the behaviour of the (smaller mass) core is relatively unaffected by HD cooling.