Observational Signatures of the First Quasars

We study the observational signatures of a potential population oflow-luminosity quasars at high redshifts in a LambdaCDM cosmology. We derivethe evolution of the quasar luminosity function at fainter luminosities andhigher redshifts than currently detected, based on three assumptions: (1) theformation of dark-matter halos follows the Press-Schechter theory, (2) theratio 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 thata universal light-curve provides an excellent fit to the observed quasarluminosity function at redshifts 2.6 < z < 4.5. By extrapolating the evolutionof this luminosity function to higher redshifts (4.5 < z < 20), we find thatthe associated early population of low-luminosity quasars reionizes theuniverse around redshift z=12. The reprocessing of the UV light of thesequasars by dust from early type II supernovae, distorts the microwavebackground spectrum by a Compton y-parameter, y = 1e-5, comparable to the upperlimit set by COBE. The Next Generation Space Telescope could detect tens ofquasars from redshifts z > 10 per square arcminute, with its proposed 1nJysensitivity at 1-3.5 microns. Absorption spectra of several such quasars wouldreveal the reionization history of the universe.Comment: 28 pages, latex, 9 figures included, submitted to Ap