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Keiichi Kodaira, Yoshiaki Taniguchi, Nobunari Kashikawa, Norio Kaifu, Hiroyasu Ando, Hiroshi Karoji, Masaru Ajiki, Masayuki Akiyama, Kentaro Aoki, Mamoru Doi, Shinobu S. Fujita, Hisanori Furusawa, Tomoki Hayashino, Masatoshi Imanishi, Fumihide Iwamuro, Masanori Iye, Koji S. Kawabata, Naoto Kobayashi, Tadayuki Kodama, Yutaka Komiyama, George Kosugi, Yuichi Matsuda, Satoshi Miyazaki, Yoshihiko Mizumoto, Kentaro Motohara, Takashi Murayama, Tohru Nagao, Kyoji Nariai, Kouji Ohta, Youichi Ohyama, Sadanori Okamura, Masami Ouchi, Toshiyuki Sasaki, Kazuhiro Sekiguchi, Kazuhiro Shimasaku, Yasunori Shioya, Tadafumi Takata, Hajime Tamura, Hiroshi Terada, Masayuki Umemura, Tomonori Usuda, Masafumi Yagi, Toru Yamada, Naoki Yasuda, Michitoshi Yoshida, The Discovery of Two Lyman α Emitters beyond Redshift 6 in the Subaru Deep Field,, Publications of the Astronomical Society of Japan, Volume 55, Issue 2, 25 April 2003, Pages L17–L21, https://doi.org/10.1093/pasj/55.2.L17
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Abstract
We performed a deep optical imaging survey using a narrow-band filter (NB921) centered at |$\lambda = 9196 \,$|Å together with |$i^\prime$| and |$z^\prime$| broadband filters covering an |$814 \,\mathrm{arcmin}^2$| area of the Subaru Deep Field. We obtained a sample of 73 strong NB921-excess objects based on the following two color criteria:|$z^\prime-\mathit{NB}\,921 \gt 1$||$z^\prime-\mathit{NB}\,921 \gt 1$| and |$i^\prime-z^\prime \gt 1.3$||$i^\prime-z^\prime \gt 1.3$|. We then obtained optical spectroscopy of nine objects in our NB921-excess sample, and identified at least two Ly|$\alpha$| emitters at |$z=6.541 \pm 0.002$| and |$z=6.578 \pm 0.002$|, 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; |$\rho_\mathrm{SFR} \sim 5.2 \times 10^{-4} \,{{{M}_{\odot}}} \,\mathrm{yr}^{-1} \,\mathrm{Mpc}^{-3}$|. 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 |$z \sim 6.6$|.
