Abstract
We performed a deep optical imaging survey using a narrow-band filter (NB 921) centered at λ = 9196 Å together with i′ and z′ broadband filters covering an 814 arcmin2 area of the Subaru Deep Field. We obtained a sample of 73 strong NB 921-excess objects based on the following two color criteria: z′ - NB921 > 1 and i′ - z′ > 1.3. We then obtained optical spectroscopy of nine objects in our NB 921 -excess sample, and identified at least two Ly α emitters at z = 6.541 ± 0.002 and z = 6.578 ± 0.002, each of which shows the characteristic sharp cutoff together with continuum depression at wavelengths shortward of the line peak. The latter object is more distant than HCM-6A at z = 6.56, which is the most distant known object that has been found so far. These new data allow us to estimate the first meaningful lower limit of the star-formation rate density beyond redshift 6; ρSFR ∼ 5.2 × 10-4 M⊙ yr-1 Mpc-3. Since it is expected that the actual density is several times higher than this value, our new observation reveals that a moderately high level of star formation activity already occurred at z ∼ 6.6.
Original language | English |
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Pages (from-to) | L17-L21 |
Journal | Publications of the Astronomical Society of Japan |
Volume | 55 |
Issue number | 2 |
DOIs | |
Publication status | Published - 2003 |
Keywords
- Cosmology: observations
- Early universe
- Galaxies: evolution
- Galaxies: formation
- Galaxies: starburst
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science