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Published July 2020 | Submitted + Published
Journal Article Open

ALPINE−ALMA [C II] Survey: on the nature of an extremely obscured serendipitous galaxy

Abstract

We report the serendipitous discovery of a dust-obscured galaxy observed as part of the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [C II] at Early times (ALPINE). While this galaxy is detected both in line and continuum emissions in ALMA Band 7, it is completely dark in the observed optical/near-infrared bands and only shows a significant detection in the UltraVISTA K_s band. We discuss the nature of the observed ALMA line, that is [C II] at z ∼ 4.6 or high-J CO transitions at z ∼ 2.2. In the first case, we find a [C II]/FIR luminosity ratio of log(L_([CII])/L_(FIR))∼−2.5⁠, consistent with the average value for local star-forming galaxies (SFGs). In the second case instead, the source would lie at larger CO luminosities than those expected for local SFGs and high-z submillimetre galaxies. At both redshifts, we derive the star formation rate (SFR) from the ALMA continuum and the physical parameters of the galaxy, such as the stellar mass (M*), by fitting its spectral energy distribution. Exploiting the results of this work, we believe that our source is a 'main-sequence', dusty SFG at z = 4.6 (i.e. [C II] emitter) with log(SFR/M_⊙ yr⁻¹) ∼ 1.4 and log(M*/M_⊙) ∼ 9.9. As a support to this scenario our galaxy, if at this redshift, lies in a massive protocluster recently discovered at z ∼ 4.57, at only ∼1 proper Mpc from its centre. This work underlines the crucial role of the ALPINE survey in making a census of this class of objects, in order to unveil their contribution to the global SFR density at the end of the Reionization epoch.

Additional Information

© 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2020 May 27. Received 2020 May 26; in original form 2020 January 31. Published: 04 June 2020. This paper is based on data obtained with the ALMA observatory, under the Large Program 2017.1.00428.L. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, Associated Universities, Inc. (AUI)/National Radio Astronomy Observatory (NRAO) and NAOJ. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under ESO programme ID 179.A-2005 and on data products produced by CALET and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium. This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Centro de Astrobiología (CAB/INTA), partnered with the University of California Observatories at Santa Cruz (UCO/Lick,UCSC). We thank D. Liu and collaborators for providing us individual values of CO and FIR luminosities estimated in their work. SB, AC, CG, FL, FP, GR, and MT acknowledge the support from grant PRIN MIUR 2017. LV acknowledges funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no. 746119. DR acknowledges support from the National Science Foundation under grant numbers AST-1614213 and AST-1910107 and from the Alexander von Humboldt Foundation through a Humboldt Research Fellowship for Experienced Researchers. GCJ acknowledges ERC Advanced grant 695671 'QUENCH' and support by the Science and Technology Facilities Council (STFC). SF is supported by the Cosmic Dawn Center of Excellence founded by the Danish National Research Foundation under the grant no. 140. EI acknowledges partial support from FONDECYT through grant number  1171710. JDS was supported by JSPS KAKENHI grant number JP18H04346, and the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan.

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Additional details

Created:
August 19, 2023
Modified:
October 20, 2023