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

A. P.S. Hygate, J. A. Hodge, E. Da Cunha, M. Rybak, S. Schouws, H. Inami, M. Stefanon, L. Graziani, R. Schneider, P. Dayal, R. J. Bouwens, R. Smit, R. A.A. Bowler, R. Endsley, V. Gonzalez, P. A. Oesch, D. P. Stark, H. S.B. Algera, M. Aravena, L. BarrufetA. Ferrara, Y. Fudamoto, J. H.A. Hilhorst, I. De Looze, T. Nanayakkara, A. Pallottini, D. A. Riechers, L. Sommovigo, M. W. Topping, P. Van Der Werf

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4 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)1775-1795
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 13 Jul 2023


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