Program: GN-2017B-FT-3

We propose GMOS spectroscopy for a newly discovered sample of four intensely Lya-emitting galaxies (rest-frame Lya EW = 240-500A) at z=4-5. These large Lya EW galaxies (LLEGs) are good candidates of high-redshift metal-poor, extremely young galaxies such as a few Myr stellar population with metallicity of only Z~0.001 that is as low as those of previously identified the most metal-poor local galaxies including I Zw 18 (Z~0.0006) or possibly even lower. These LLEGs are identified in the latest Subaru Hyper Suprime-Cam (HSC) survey data, whose effective volume is more than ten times larger than previous narrowband Lya emitter searches. We carefully remove transients from our sample by checking multi-epoch observation images. However, without spectroscopy, we cannot certainly rule out the other possibilities of low-z line emitters and faint AGNs. With the GMOS spectra, we will spectroscopically confirm our LLEGs at high redshifts and examine the presence of AGN signatures. We will derive the number densities of this very rare population, which will be useful to constrain the duty cycle of intermittent star formation activities. Our spectroscopy program will yield a unique sample of high-redshift galaxies in an early phase of galaxy formation that have been poorly explored so far.