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

Hygate, APS, Hodge, JA, Da Cunha, E, Rybak, M, Schouws, S, Inami, H, Stefanon, M, Graziani, L, Schneider, R, Dayal, P, Bouwens, RJ, Smit, R, Bowler, RAA, Endsley, R, Gonzalez, V, Oesch, PA, Stark, DP, Algera, HSB, Aravena, M, Barrufet, L , Ferrara, A, Fudamoto, Y, Hilhorst, JHA, De Looze, I, Nanayakkara, T, Pallottini, A, Riechers, DA, Sommovigo, L, Topping, MW and Van Der Werf, P (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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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)
SWORD Depositor: A Symplectic
Date Deposited: 12 Dec 2023 13:06
Last Modified: 12 Dec 2023 13:15
DOI or ID number: 10.1093/mnras/stad1212
URI: https://researchonline.ljmu.ac.uk/id/eprint/22084
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