Relative Role of Stars and Quasars in Cosmic Reionization

Understand

We revisit the classical view that quasar contribution to the reionization of hydrogen is unimportant.

• When secondary ionization are taken into account, in many plausible scenarios for the formation and growth of supermassive black holes quasars contribute substantially or even dominantly at z>8, although their contribution generally falls below that of star-forming galaxies by z=6.
• Theoretical models that guide the design of the first generation of redshifted 21 cm experiments must, therefore, substantially account for the quasar contribution in order to be even qualitatively accurate.