Observational Signatures of the First Quasars

We study the observational signatures of a potential population of low-luminosity quasars at high redshifts in a LambdaCDM cosmology. We derive the evolution of the quasar luminosity function at fainter luminosities and higher redshifts than currently detected, based on three assumptions: (1) the formation of dark-matter halos follows the Press-Schechter theory, (2) the ratio of central black hole mass to halo mass is the same for all halos, and (3) the light-curve of quasars, in Eddington units, is universal. We show that a universal light-curve provides an excellent fit to the observed quasar luminosity function at redshifts 2.6 10 per square arcminute, with its proposed 1nJy sensitivity at 1-3.5 microns. Absorption spectra of several such quasars would reveal the reionization history of the universe.