High-redshift Ly$\mathsf{\alpha}$ emitters with a large equivalent width

Abstract

We report new follow-up spectroscopy of -dropout galaxies with an NB921-band depression found in the Subaru Deep Field. The NB921-depressed -dropout selection method is expected to select galaxies with large equivalent-width Lyα emission over a wide redshift range, . Two of four observed targets show a strong emission line with a clear asymmetric profile, identified as Lyα emitters at z = 6.11 and 6.00. Their rest-frame equivalent widths are 153 and 114 , which are lower limits on the intrinsic equivalent widths. Through our spectroscopic observations (including previous ones) of NB921-depressed -dropout galaxies, we identified 5 galaxies in total with a rest-frame equivalent width larger than 100 at out of 8 photometric candidates, which suggests that the NB921-depressed -dropout selection method is possibly an efficient way to search for Lyα emitters with a large Lyα equivalent width, in a wider redshift range than with usual narrow-band excess techniques. By combining these findings with our previous observational results, we infer that the fraction of broad-band selected galaxies having a rest-frame equivalent width larger than 100 is significantly higher at (the cosmic age of ~1 Gyr) than that at (~2 Gyr), being consistent with the idea that the typical stellar population of galaxies is significantly younger at than that at . The NB921-depressed -dropout galaxies may be interesting candidates for hosts of massive, zero-metallicity Population III stars.