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We investigate the high-redshift quasar luminosity function (QLF) down to an apparent magnitude of I(AB) = 25 in the Cosmic Evolution Survey (COSMOS). Careful analysis of the extensive COSMOS photometry and imaging data allows us to identify and remove stellar and low-redshift contaminants, enabling a selection that is nearly complete for type-1 quasars at the redshifts of interest. We find 155 likely quasars at z > 3.1, 39 of which have prior spectroscopic confirmation. We present our sample in detail and use these confirmed and likely quasars to compute the rest-frame UV QLF in the redshift bins 3.1 < z < 3.5 and 3.5 < z < 5. The space density of faint quasars decreases by roughly a factor of four from z sim 3.2 to z sim 4, with faint-end slopes of {beta} sim -1.7 at both redshifts. The decline in space density of faint optical quasars at z > 3 is similar to what has been found for more luminous optical and X-ray quasars. We compare the rest-frame UV luminosity functions found here with the X-ray luminosity function at z > 3, and find that they evolve similarly between z sim 3.2 and z sim 4; however, the different normalizations imply that roughly 75% of X-ray bright active galactic nuclei (AGN) at z sim 3 - 4 are optically obscured. This fraction is higher than found at lower redshift and may imply that the obscured, type-2 fraction continues to increase with redshift at least to z sim 4. Finally, the implications of the results derived here for the contribution of quasars to cosmic reionization are discussed.
We present the result of our low-luminosity quasar survey in the redshift range of 4.5 < z < 5.5 in the COSMOS field. Using the COSMOS photometric catalog, we selected 15 quasar candidates with 22 < i < 24 at z~5, that are ~ 3 mag fainter than the SD
We searched for quasars that are ~ 3 mag fainter than the SDSS quasars in the redshift range 3.7 < z < 4.7 in the COSMOS field to constrain the faint end of the quasar luminosity function. Using optical photometric data, we selected 31 quasar candida
We have conducted a spectroscopic survey to find faint quasars (-26.0 < M_{1450} < -22.0) at redshifts z=3.8-5.2 in order to measure the faint end of the quasar luminosity function at these early times. Using available optical imaging data from porti
We present the quasar luminosity function at $z sim 5$ derived from the optical wide-field survey data obtained as a part of the Subaru strategic program (SSP) with Hyper Suprime-Cam (HSC). From $sim$81.8 deg$^2$ area in the Wide layer of the HSC-SSP
(abridged) We report the UV luminosity function (LF) of Lyman break galaxies at z~5 derived from a deep and wide survey using the Subaru/Suprime-Cam. Target fields consist of two blank regions of the sky (the HDF-N and J0053+1234), and the total effe