The Subaru Deep Field Project : Lyman Α Emitters at Redshift of 6

We present new results of a deep optical imaging survey using a narrowband filter (NB921) centered at λ = 9196 Å together with B, V , R, i, and z broadband filters in the sky area of the Subaru Deep Field which has been promoted as one of legacy programs of the 8.2m Subaru Telescope. We obtained a photometric sample of 58 Lyα emitter candidates at z ≈ 6.5 – 6.6 among ∼ 180 strong NB921-excess (z − NB921 > 1.0) objects together with a color criterion of i − z > 1.3. We then obtained optical spectra of 20 objects in our NB921-excess sample and identified at least nine Lyα emitters at z ∼ 6.5 – 6.6 including the two emitters reported by Kodaira et al. (2003). Since our Lyα emitter candidates are free from strong amplification of gravitational lensing, we are able to discuss their observational properties from a statistical point of view. Based on these new results, we obtain a lower limit of the star formation rate density of ρSFR ≃ 5.5× 10 −4 h0.7 M⊙ yr −1 Mpc at z ≈ 6.6, being consistent with our previous estimate. We discuss the nature of star-formation activity in galaxies beyond z = 6. Subject headings: cosmology: observations — early universe — galaxies: starburst — galaxies: formation — galaxies: evolution