(Proposal ID) S17A-063

(PI) Ono, Yoshiaki

(Proposal Title)
Spectroscopy for Very Bright z ~ 6-7 Galaxies Found in 200 deg^2 HSC Data

(Abstract)
We propose deep FOCAS spectroscopy for very bright and rare dropout galaxy 
candidates at z ~ 6-7 found in early data products of the Subaru strategic 
program with Hyper Suprime-Cam (HSC SSP). The survey area is ~ 200 deg^2, 
which is more than 50 times larger than previous work. From the HSC SSP data, 
we select very bright z ~ 6-7 dropout galaxy candidates with -23.5 < M_{UV}  
< -22.7 mag. In particular, we find a remarkable candidate of the z=6 brightest
gravitationally lensed galaxy. In addition, our three brightest z ~ 7 
candidates are more luminous than the spectroscopically confirmed galaxies at 
similar redshifts by more than 0.9 mag. We carefully remove contaminants such 
as spurious sources and moving objects from our sample by checking multi-epoch 
observation images. Since we have completed all the screenings possible with 
the imaging data, the next step is to test the candidates with spectroscopy. 
Following our initial successful short service observations, we propose this 
normal program of FOCAS spectroscopy. Our FOCAS observations will enable us to 
spectroscopically confirm very bright z~ 6-7 galaxies and to obtain the first 
reliable measurements of the z ~ 6-7 UV luminosity functions at the unexplored 
bright magnitude range.