(Proposal ID) S17B-140

(PI) Koptelova, Ekaterina

(Proposal Title)
Spectroscopy of new z>6.5 quasar candidates selected from PS1&WISE

(Abstract)
We propose FOCAS spectroscopy of z$>$6.5 QSO candidates selected over 20,000 
sq. deg. using data from the new PanSTARRS1 3pi survey combined with the mid-
infrared WISE data. PanSTARRS1 has near-infrared 'y' band which allows for 
detecting Lyman alpha emission of QSOs at redshifts  z = 6.5 - 7.2. This 
redshift range is the frontier with only 8 known QSOs (one of which was 
discovered by us). Our goal is to increase the sample of known QSOs at z>6.5 
which is crucial for understanding of the reionization epoch. We implemented a 
new approach of candidate selection based on the PS1-WISE colors of high-
redshift QSOs, and an additional requirement of their multi-epoch detections 
in the PS1 y band. This approach is significantly more efficient than using 
color selection criteria alone. We found 15 promising candidates. All of them 
are clear z-band dropouts (detected only in the y band) and appear to be much 
bluer in the y-W1 and y-W2 colors compared to their major contaminating 
sources, the L and T dwarfs.