HII Bubble Growth during Reionization

We investigate the growth of cosmological HII bubbles during reionization based on a cosmological radiative transfer simulation. We find that the number distribution of bubble volume has a maximum at $∼0.6 Mpc3/h3.$ Population III stars are as important as Population II stars in producing ionizing photons However, at $z⩽8,$ Population II stars become a dominant source of ionizing photons. We also find that the clustering of dark matter halos is a main factor to determine the size of large HII bubbles. For small bubbles, Population III stars provide most of ionizing photons. These highly‐biased HII bubbles result in a strong non‐gaussianity in the HII field.