ALMA deep field in SSA22: Blindly detected CO emitters and [C II] emitter candidates
Smail, Ian; Fujimoto, Seiji; Inoue, Akio K.; Tamura, Yoichi; Kohno, Kotaro; Iono, Daisuke; Kawabe, Ryohei; Yamada, Toru; Yamaguchi, Yuki; Hatsukade, Bunyo; Kubo, Mariko; Nagao, Tohru; Izumi, Takuma; Lee, Minju; Takeuchi, Tsutomu T.; Nakanishi, Kouichiro; Ao, Yiping; Umehata, Hideki; Matsuda, Yuichi; Yoshida, Naoki; Ikarashi, Soh; Ivison, Rob; Swinbank, A. Mark; Hayatsu, Natsuki H.
Japan, United Kingdom, Germany, Netherlands
Abstract
We report the identification of four millimeter line-emitting galaxies with the Atacama Large Milli/submillimeter Array (ALMA) in SSA22 Field (ADF22). We analyze the ALMA 1.1-mm survey data, with an effective survey area of 5 arcmin2, frequency ranges of 253.1-256.8 and 269.1-272.8 GHz, angular resolution of 0{^''.}7 and rms noise of 0.8 mJy beam-1 at 36 km s-1 velocity resolution. We detect four line-emitter candidates with significance levels above 6σ. We identify one of the four sources as a CO(9-8) emitter at z = 3.1 in a member of the proto-cluster known in this field. Another line emitter with an optical counterpart is likely a CO(4-3) emitter at z = 0.7. The other two sources without any millimeter continuum or optical/near-infrared counterpart are likely to be [C II] emitter candidates at z = 6.0 and 6.5. The equivalent widths of the [C II] candidates are consistent with those of confirmed high-redshift [C II] emitters and candidates, and are a factor of 10 times larger than that of the CO(9-8) emitter detected in this search. The [C II] luminosity of the candidates are 4-7 × 108 L⊙. The star formation rates (SFRs) of these sources are estimated to be 10-20 M⊙ yr-1 if we adopt an empirical [C II] luminosity-SFR relation. One of them has a relatively low S/N ratio, but shows features characteristic of emission lines. Assuming that at least one of the two candidates is a [C II] emitter, we derive a lower limit of [C II]-based star formation rate density (SFRD) at z ∼ 6. The resulting value of >10-2 M⊙ yr-1 Mpc-3 is consistent with the dust-uncorrected UV-based SFRD. Future millimeter/submillimeter surveys can be used to detect a number of high-redshift line emitters, with which to study the star formation history in the early universe.