(Proposal ID) S17A-160

(PI) Akiyama, Masayuki

(Proposal Title)
Shape of the broad-line QSO luminosity function in the early universe

(Abstract)
Cosmological evolution of the AGN luminosity function (LF) at z>3 is a 
fundamental observable to statistically unveil the accretion growth history 
of Super Massive Black Holes (SMBHs) in the early universe. Furthermore, 
constraints on the faint-end slope of the LF are also important to evaluate 
contribution of AGNs to the UV ionizing background in the reionization era. 
The wide and deep imaging data from the HSC SSP program provide us a unique 
opportunity to determine the shape of the QSO LF in the early universe with 
unprecedented accuracy. The newly derived QSO LF at z=4 shows stronger break 
and flatter slope in the faint end than the LFs in literature, suggesting much 
smaller contribution to the ionizing photon budget. However, the new LF relies 
on the photometric selection of z=4 QSOs, and, here, we would like to evaluate 
contamination rate, redshift distribution, and completeness of the selection 
with the proposed spectroscopic follow-up of a sub-sample of the candidates. 
Once we establish the method to derive the QSO LF from the HSC photometric 
dataset, we can extend the study to lower (z=3) and higher (z=5) redshifts to 
disclose the discussion on the redshift evolution of the QSO LF in the early 
universe.