(Proposal ID) S15B-075

(PI) Ouchi, Masami

(Proposal Title)
MOSFIRE Spectroscopy for the Highest-z Subaru LAE Candidates III

(Abstract)
We propose MOSFIRE spectroscopy for our z=7.3 Lyalpha emitter (LAE) candidates 
found by our 100-hour Subaru imaging survey. Our spectroscopy will complete 
the previously approved, but weathered-out, programs of S13B-004 and S14B-068 
to identify three remaining candidates with Lyalpha, and extend our LAE study 
to measure the systemic velocity  with C[iii]1907,1909 doublets for one bright 
LAE target. We have two scientific goals. First is to examine the rapid 
decrease of Lyalpha luminosity function from z=6.6 to 7.3 (Konno et al. 2014) 
that is clue for understanding galaxy formation and reionization including a 
possibility of accelerating increase of HI beyond z~7. Because this conclusion 
is based on our photometric LAE sample with unclear systematics, we test the 
conclusion with spectroscopically-confirmed LAEs, where one of our photometric 
LAEs has been successfully confirmed in the S13B and S14B runs. Second is to 
examine the evolution of Lyalpha velocity offset, Delta v_{Lyalpha}, of LAEs 
with the Lyalpha and systemic C{iii] velocities for the reionization 
interpretation. It will be the first step for measuring Delta v_{Lyalpha} of 
z~7 LAEs that are, in practice, used for the x_{HI} estimate in our Lyalpha 
LF analysis, complementing the Delta v_{Lyalpha} values obtained for dropout 
galaxies at z=6-7 (Stark et al. 2014).