Spectroscopy of i-Dropout Galaxies with an NB921-Band Depression in the Subaru Deep Field

We report new spectroscopy of two star-forming galaxies with strong Ly(alpha) emission at z = 6.03 and 6.04 in the Subaru Deep Field. These two objects are originally selected as iʹ-dropouts (iʹ - ziʹ > 1.5) showing an interesting photometric property, the "NB921 depression." The NB921-band (centered at 9196 ?) magnitude is significantly depressed with respect to the ziʹ-band magnitude. The optical spectra of these two objects exhibit asymmetric emission lines at iʹobs ~8540 and ~8560 ?, suggesting that these objects are Ly(alpha) emitters at z ~6. The rest-frame equivalent widths of the Ly(alpha) emission of the two objects are 94 and 236 ?; the latter is the Ly(alpha) emitter with the largest Ly(alpha) equivalent width at z >6 ever spectroscopically confirmed. The spectroscopically measured Ly(alpha) fluxes of these two objects are consistent with the interpretation that the NB921 depression is caused by the contribution of the strong Ly(alpha) emission to the ziʹband flux. Most of the NB921-depressed iʹ-dropout objects are thought to be strong Ly(alpha) emitters at 6.0 6.6 do not dominate the NB921-depressed iʹ-dropout sample. Thus, the NB921-depression method is very useful for finding high-z Ly(alpha) emitters with a large Ly(alpha) equivalent width over a large redshift range, 6.0 6 to z ~3.