(Proposal ID) S17A-006

(PI) Kashikawa, Nobunari

(Proposal Title)
Deep Near-IR Spectroscopy of the Most Distant Galaxy Known at z=11.09

(Abstract)
We propose to use Keck MOSFIRE to carry out deep K-band spectroscopy of the 
galaxy GN-z11 at z=11.09_{-0.12}^{+0.08}. GN-z11 is the most distant galaxy 
known (Oesch et al. 2016). It is surprisingly bright; theoretical models 
predicted that a search volume 10--50 times larger would have been necessary 
to find one such galaxy. Therefore, the discovery of GN-z11 sheds new light on 
galaxy formation in the early universe. However, the available information for 
this galaxy is very limited so far. The proposed observations will 
simultaneously cover the wavelength range that allows the detection of 
HeII (1640Angstrom) and CIII] (1909Angstrom), the most prominent emission 
lines expected to be seen in the observed range. HeII has been long suggested 
as a direct probe of metal-free Population III (Pop III) massive stars. 
CIII] has been claimed as an alternative to identify galaxies at z>6, as it 
does not suffer from radiative transfer effects like Lyalpha. The detection 
of these lines will enable us to compute accurate redshift, calculate line 
flux, measure Pop III star formation rate, estimate ionizing state of the 
galaxy, and so on. In particular, we will directly detect the possible 
signature of Pop III stars in a galaxy at z>11. Any non-detections will 
put very strong upper limits on the measurements mentioned above.