Astronomy and Astrophysics, volume 468, 877-883 (2007/6-4)
High-redshift Lyα emitters with a large equivalent width. Properties of i'-dropout galaxies with an NB921-band depression in the Subaru Deep Field.
NAGAO T., MURAYAMA T., MAIOLINO R., MARCONI A., KASHIKAWA N., AJIKI M., HATTORI T., LY C., MALKAN M.A., MOTOHARA K., OHTA K., SASAKI S.S., SHIOYA Y. and TANIGUCHI Y.
Abstract (from CDS):
We report new follow-up spectroscopy of i'-dropout galaxies with an NB921-band depression found in the Subaru Deep Field. The NB921-depressed i'-dropout selection method is expected to select galaxies with large equivalent-width Lyα emission over a wide redshift range, 6.0≲z≲6.5. 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 153Å and 114Å, which are lower limits on the intrinsic equivalent widths. Through our spectroscopic observations (including previous ones) of NB921-depressed i'-dropout galaxies, we identified 5 galaxies in total with a rest-frame equivalent width larger than 100Å at 6.0≲z≲6.5 out of 8 photometric candidates, which suggests that the NB921-depressed i'-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 100Å is significantly higher at z∼6 (the cosmic age of ∼1Gyr) than that at z∼3 (∼2Gyr), being consistent with the idea that the typical stellar population of galaxies is significantly younger at z∼6 than that at z∼3. The NB921-depressed i'-dropout galaxies may be interesting candidates for hosts of massive, zero-metallicity Population III stars.
cosmology: early universe - galaxies: evolution - galaxies: formation - galaxies: individual: J132345.6+271701 - galaxies: individual: J132519.4+271829 - galaxies: starburst
Table 1: [NTK2004] SDF JHHMMSS.s+DDMMSS N=5 added.
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