{
  "id": "2304.09206",
  "version": "v1",
  "published": "2023-04-18T18:00:41.000Z",
  "updated": "2023-04-18T18:00:41.000Z",
  "title": "The ALMA REBELS Survey: Discovery of a massive, highly star-forming and morphologically complex ULIRG at $z =7.31$",
  "authors": [
    "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. Barrufet",
    "A. Ferrara",
    "Y. Fudamoto",
    "J. H. A",
    "I. De Looze",
    "T. Nanayakkara",
    "A. Pallottin",
    "D. A. Riechers",
    "L. Sommovigo",
    "M. W. Topping",
    "P. van der Werf"
  ],
  "comment": "Accepted for publication in MNRAS. 21 pages, 8 figures",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We present Atacama Large Millimeter/Submillimeter Array (ALMA) [CII] and $\\sim158$ $\\rm\\mu m$ continuum observations of REBELS-25, a massive, morphologically complex ultra-luminous infrared galaxy (ULIRG; $L_{\\rm IR}=1.5^{+0.8}_{-0.5}\\times10^{12}$ L$_\\odot$) 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 $M_{*}=8^{+4}_{-2}\\times10^{9}$ M$_\\odot$. From dust-continuum and ultraviolet observations, we determine a total obscured + unobscured star formation rate of SFR $=199^{+101}_{-63}$ M$_\\odot$ yr$^{-1}$. This is about four times the SFR estimated from an extrapolated main-sequence. We also infer a [CII]-based molecular gas mass of $M_{\\rm H_2}=5.1^{+5.1}_{-2.6}\\times10^{10}$ $M_\\odot$, implying a molecular gas depletion time of $ t_{\\rm depl, H_2}=0.3^{+0.3}_{-0.2}$ Gyr. We observe a [CII] 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 [CII] emission at large positive velocities ($\\sim500$ 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 M$_\\odot$ yr$^{-1}$, which is consistent with expectations for a star formation-driven outflow. Given its large stellar mass, SFR and molecular gas reservoir $\\sim700$ 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 $z\\sim4$.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-04-18T18:00:41.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "alma rebels survey",
      "morphologically complex ulirg",
      "declining star formation history",
      "molecular gas",
      "complex ultra-luminous infrared galaxy"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 21,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}