New Constraints on the Molecular Gas in the Prototypical HyLIRGs BRI1202-0725 and BRI1335-0417

Abstract

We present Karl G Jansky Very Large Array observations of CO(J=2\to 1) line emission and rest-frame 250 GHz continuum emission of the Hyper-Luminous IR Galaxies (HyLIRGs) BRI 1202-0725 (z = 4.69) and BRI 1335-0417 (z = 4.41), with an angular resolution as high as 0.″15. Our low-order CO observations delineate the cool molecular gas, the fuel for star formation in the systems, in unprecedented detail. For BRI 1202-0725, line emission is seen from both extreme starburst galaxies: the quasar host and the optically obscured submm galaxy (SMG), in addition to one of the Lyα emitting galaxies in the group. Line emission from the SMG shows an east-west extension of about 0.″6. For Lyα-2, the CO emission is detected at the same velocity as [C II] and [N II], indicating a total gas mass ∼4.0 × 10¹⁰ M _⊙. The CO emission from BRI 1335-0417 peaks at the nominal quasar position, with a prominent northern extension (∼1″, a possible tidal feature). The gas depletion timescales are ∼10⁷ years for the three HyLIRGs, consistent with extreme starbursts, while that of Lyα-2 may be consistent with main sequence galaxies. We interpret these sources as major star formation episodes in the formation of massive galaxies and supermassive black holes via gas-rich mergers in the early universe.