Relative Role of Stars and Quasars in Cosmic Reionization
  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.
