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ALMA Deep Field in SSA22

Umehata, Hideki; Smail, Ian; Swinbank, A.M.; Kohno, Kotaro; Tamura, Yoichi; Wang, Tao; Ao, Yiping; Hatsukade, Bunyo; Kubo, Mariko; Nakanishi, Kouchiro; Hayatsu, Natsuki N.

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Hideki Umehata

Kotaro Kohno

Yoichi Tamura

Tao Wang

Yiping Ao

Bunyo Hatsukade

Mariko Kubo

Kouchiro Nakanishi

Natsuki N. Hayatsu


Deep surveys with the Atacama Large Millimeter Array (ALMA) have uncovered a population of dusty star-forming galaxies which are faint or even undetected at optical to near-infrared wavelengths. Their faintness at short wavelengths makes the detailed characterization of the population challenging. Here we present a spectroscopic redshift identification and a characterization of one of these near-infrared-dark galaxies discovered by an ALMA deep survey. The detection of [C i](1–0) and CO(4–3) emission lines determines the precise redshift of the galaxy, ADF22.A2, to be z = 3.9913 ± 0.0008. On the basis of a multi-wavelength analysis, ADF22.A2 is found to be a massive, star-forming galaxy with a stellar mass of M∗ = 1.1 +1.3 −0.6 × 1011 M and SFR= 430+230 −150 M yr−1 . The molecular gas mass was derived to be M(H2) [CI] = (5.9 ± 1.5) × 1010 M, indicating a gas fraction of ≈35%, and the ratios of L[CI](1−0)/LIR and L[CI](1−0)/LCO(4−3) suggest that the nature of the interstellar medium in ADF22.A2 is in accordance with those of other bright submillimeter galaxies. The properties of ADF22.A2, including the redshift, star-formation rate, stellar mass, and depletion time scale (τdep ≈ 0.1−0.2 Gyr), also suggest that ADF22.A2 has the characteristics expected for the progenitors of quiescent galaxies at z & 3. Our results demonstrate the power of ALMA contiguous mapping and line scan, which help us to obtain an unbiased view of galaxy formation in the early Universe.

Journal Article Type Article
Acceptance Date Jul 12, 2020
Online Publication Date Aug 3, 2020
Publication Date 2020-08
Deposit Date Aug 19, 2020
Publicly Available Date Aug 19, 2020
Journal Astronomy and astrophysics.
Print ISSN 0004-6361
Electronic ISSN 1432-0746
Publisher EDP Sciences
Peer Reviewed Peer Reviewed
Volume 640
Article Number L8
Public URL


Published Journal Article (1.9 Mb)

Copyright Statement
Umehata, Hideki, Smail, Ian, Swinbank, A. M., Kohno, Kotaro, Tamura, Yoichi, Wang, Tao, Ao, Yiping, Hatsukade, Bunyo, Kubo, Mariko, Nakanishi, Kouchiro & Hayatsu, Natsuki N. (2020). ALMA Deep Field in SSA22. Astronomy & Astrophysics 640: L8, reproduced with permission, © ESO.

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