The ALMA REBELS Survey

discovery of a massive, highly star-forming, and morphologically complex ULIRG at z = 7.31

Journal article (2023)

Authors

A. P.S. Hygate Universiteit Leiden
J. A. Hodge Universiteit Leiden
E. Da Cunha University of Western Australia, Arc Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)
M. Rybak Education Support , Universiteit Leiden
S. Schouws Universiteit Leiden
H. Inami Hiroshima University
M. Stefanon Universiteit Leiden, Universidad de Valencia (ICMol)
L. Graziani Sapienza University of Rome, INAF-Osservatorio Astrofisico di Arcetri
R. Schneider Sapienza University of Rome, University of Roma Tre, INAF/Osservatorio Astronomico di Roma
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Galaxies: ISM Galaxies: high-redshift Galaxies: star formation Galaxies: evolution ISM: jets and outflows
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Published Date

2023

Language

English

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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.