(Proposal ID) S15B-094

(PI) Koptelova, Ekaterina

(Proposal Title)
A survey for z>6.5 QSOs in the PanSTARRS1 stack images

(Abstract)
High-redshift QSOs are highly important objects in various scientific aspects. 
For example, their spectra will reveal the onset of reionization of the 
intergalactic medium (Gunn-Peterson trough). We propose FOCAS spectroscopy of 
QSO candidates at 6.5<z<7.0 carefully selected from PanSTARRS1. Approaching 
the Planck reionization epoch of z=8.8, this redshift range is the frontier 
with only 7 known QSOs, and it is important to increase the sample due to the 
large cosmic variance. At z>6.5, Lyalpha emission of QSOs moves out of the z 
into the y band. Therefore, to find a QSO at 6.5<z<7.0, a large survey in both 
optical z band and near-IR y band is necessary. The Pan-STARRS1 provides a 
large enough area coverage (30000 deg^2) in z and y to find ~60 QSOs, which 
are bright enough for cosmic reionization studies (y<21 mag). We used the new 
target selection method proposed by Venemans et al. (2015), which achieved the 
spectroscopic success rate of 100% by combining the PanSTARRS1 and WISE mid-IR 
colors. By applying the successful target selection to less explored northern 
sky with Subaru, our project is likely to succeed.