The ALMA REBELS Survey: discovery of a massive, highly star-forming, and morphologically complex ULIRG at z = 7.31

Hygate, APS ORCID: 0000-0002-6488-471X, Hodge, JA ORCID: 0000-0001-6586-8845, Da Cunha, E ORCID: 0000-0001-9759-4797, Rybak, M ORCID: 0000-0002-1383-0746, Schouws, S ORCID: 0000-0001-9746-0924, Inami, H ORCID: 0000-0003-4268-0393, Stefanon, M ORCID: 0000-0001-7768-5309, Graziani, L ORCID: 0000-0002-9231-1505, Schneider, R ORCID: 0000-0001-9317-2888, Dayal, P ORCID: 0000-0001-8460-1564, Bouwens, RJ ORCID: 0000-0002-4989-2471, Smit, R ORCID: 0000-0001-8034-7802, Bowler, RAA ORCID: 0000-0003-3917-1678, Endsley, R ORCID: 0000-0003-4564-2771, Gonzalez, V ORCID: 0000-0002-3120-0510, Oesch, PA ORCID: 0000-0001-5851-6649, Stark, DP ORCID: 0000-0001-6106-5172, Algera, HSB ORCID: 0000-0002-4205-9567, Aravena, M ORCID: 0000-0002-6290-3198, Barrufet, L ORCID: 0000-0003-1641-6185 et al (2023) The ALMA REBELS Survey: discovery of a massive, highly star-forming, and morphologically complex ULIRG at z = 7.31. Monthly Notices of the Royal Astronomical Society, 524 (2). pp. 1775-1795. ISSN 0035-8711

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Abstract

We present Atacama Large Millimeter/Submillimeter Array (ALMA) [C ii] and ∼158 continuum observations of REBELS-25, a massive, morphologically complex ultra-luminous infrared galaxy (ULIRG; LIR = L⊙) at z = 7.31, spectroscopically confirmed by the Reionization Era Bright Emission Line Survey (REBELS) ALMA Large Programme. REBELS-25 has a significant stellar mass of. From dust-continuum and ultraviolet observations, we determine a total obscured + unobscured star formation rate of SFR. This is about four times the SFR estimated from an extrapolated main sequence. We also infer a [C ii]-based molecular gas mass of, implying a molecular gas depletion time of Gyr. We observe a [C ii] velocity gradient consistent with disc rotation, but given the current resolution we cannot rule out a more complex velocity structure such as a merger. The spectrum exhibits excess [C ii] emission at large positive velocities (∼500 km s-1), which we interpret as either a merging companion or an outflow. In the outflow scenario, we derive a lower limit of the mass outflow rate of 200, which is consistent with expectations for a star-formation-driven outflow. Given its large stellar mass, SFR, and molecular gas reservoir ∼700 Myr after the big bang, we explore the future evolution of REBELS-25. Considering a simple, conservative model assuming an exponentially declining star formation history, constant star formation efficiency, and no additional gas inflow, we find that REBELS-25 has the potential to evolve into a galaxy consistent with the properties of high-mass quiescent galaxies recently observed at z ∼4.

Item Type:	Article
Additional Information:	This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2023 the Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords:	0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press (OUP)
Date of acceptance:	3 April 2023
Date of first compliant Open Access:	12 December 2023
Date Deposited:	12 Dec 2023 13:06
Last Modified:	04 Jul 2025 15:15
DOI or ID number:	10.1093/mnras/stad1212
URI:	https://researchonline.ljmu.ac.uk/id/eprint/22084

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