Deep Observations of CO and Free-Free Emission in Ultraluminous Infrared
  QSO IRAS F07599+6508
  Infrared quasi-stellar objects (IR QSOs) are a rare subpopulation selected
from ultraluminous infrared galaxies (ULIRGs) and have been regarded as
promising candidates of ULIRG-to-optical QSO transition objects. Here we
present NOEMA observations of the CO(1-0) line and 3 mm continuum emission in
an IR QSO IRAS F07599+6508 at $z=0.1486$, which has many properties in common
with Mrk 231. The CO emission is found to be resolved with a major axis of
$\sim$6.1 kpc that is larger than the size of $\sim$4.0 kpc derived for 3 mm
continuum. We identify two faint CO features located at a projected distance of
$\sim$11.4 and 19.1 kpc from the galaxy nucleus, respectively, both of which
are found to have counterparts in the optical and radio bands and may have a
merger origin. A systematic velocity gradient is found in the CO main
component, suggesting that the bulk of molecular gas is likely rotationally
supported. Based on the radio-to-millimeter spectral energy distribution and IR
data, we estimate that about 30$\%$ of the flux at 3 mm arises from free-free
emission and infer a free-free-derived star formation rate of 77 $M_\odot\ {\rm
yr^{-1}}$, close to the IR estimate corrected for the AGN contribution. We find
a high-velocity CO emission feature at the velocity range of about -1300 to
-2000 km s$^{-1}$. Additional deep CO observations are needed to confirm the
presence of a possible very high-velocity CO extension of the OH outflow in
this IR QSO.
