The History and Morphology of Helium Reionization

Understand

A variety of observations now indicate that intergalactic helium was fully ionized by z~3.

• The most recent measurements of the high-redshift quasar luminosity function imply that these sources had produced ~2.5 ionizing photons per helium atom by that time, consistent with a picture in which the known quasar population drives HeII reionization.
• Here we describe the distribution of ionized and neutral helium gas during this era.
• Because the sources were rare and bright (with the photon budget dominated by quasars with luminosities L>L_\star), random fluctuations in the quasar population determined the morphology of ionized gas when the global ionized fraction x_i was small, with the typical radius R_c of a HeIII bubble ~15-20 comoving Mpc.