(Proposal ID) S10B-044

(PI) Iwata, Ikuru

(Proposal Title)
Revealing the nature of galaxies emitting strong Lyman continuum

(Abstract)
To understand the sources of cosmic reionization, direct observation of Lyman 
continuum (LyC) in the early universe is essentially important, and due to the 
strong evolution of average IGM opacity toward higher redshift, z ~3 is a 
unique window for this observation. We made deep narrow-band imaging 
observation of the SSA22 field, and discovered 17 spectroscopically-identified 
galaxies at z~3. They show unexpectedly strong LyC emission which is 
comparable to or exceeds the maximum LyC to non-ionizing UV flux ratio for 
standard stellar population models. The hardness of the SED suggests the 
existence of exotic sources, such as PopIII stars, and possibily significant 
contribution from nebular emission in LyC. In order to reveal the nature of 
these strong LyC sources, we propose a deep spectroscopy covering 3200 
Angstrom to 8000 Angstrom. By placing slits accurately at the LyC positions, 
we intend to obtain the spectral shape of LyC emitting regions. With the 
spectra from wavelength below Lyman limit to rest-frame UV, we aim at 
obtaining insights of the origin of strong LyC, i.e., whether the source is 
young, extremely metal poor stellar populations and how significant the 
contribution from nebular emission is. Using the Keck/LRIS is the unique 
opportunity to accomplish this observation.