부산대학교 도서관

We present Atacama Large Millimeter/Submillimeter Array (ALMA) [C  ii ] and ∼158 |$\rm \mu m$| continuum observations of REBELS-25, a massive, morphologically complex ultra-luminous infrared galaxy (ULIRG; L IR = |$1.5^{+0.8}_{-0.5} \times 10^{12}$| 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 |$M_{*} = \mbox{$ 8^{+4}_{-2} \times 10^{9} $}{} ~\mbox{M$_\odot $}{}$|⁠. From dust-continuum and ultraviolet observations, we determine a total obscured + unobscured star formation rate of SFR |$= \mbox{$199^{+101}_{-63}$}{} ~ \mbox{M$_\odot $}~ \mbox{${\rm yr}$}^{-1}$|⁠. This is about four times the SFR estimated from an extrapolated main sequence. We also infer a [C  ii ]-based molecular gas mass of |$M_{{\rm H}_{2}} = \mbox{$5.1^{+5.1}_{-2.6} \times 10^{10}$}{} ~\mbox{M$_\odot $}{}$|⁠ , implying a molecular gas depletion time of |$t_{\rm depl, {\rm H}_{2}} = \mbox{$0.3^{+0.3}_{-0.2} $}{}$| 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 |$\mbox{M$_\odot $}~ \mbox{${\rm yr}$}^{-1}$|⁠ , 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. [ABSTRACT FROM AUTHOR]