  Optical observations of the quasar J0015+1842 at z=2.6 have recently revealed
the presence of multi-phase outflowing winds intercepted by the line of sight
to the active nucleus. Here, we present 3-mm observations of this system with
the NOrthern Extended Millimeter Array (NOEMA). Our data reveals molecular gas,
traced via a Gaussian CO(3-2) line, with a remarkably large velocity dispersion
(FWHM=1014+/-120 km/s). The integrated line flux indicates a total molecular
mass in the range M_H2 ~ (3.4-17)x10^10 Msun, with the spread dominated by the
assumed CO-to-H2 conversion factor. Assuming the 3-mm continuum emission is
thermal, we derive a dust mass of Mdust ~ 2x10^9 Msun. J0015+1842 is located in
the molecular gas-rich region in the IR vs CO line luminosity diagram,
in-between the main locus of main-sequence and sub-millimeter galaxies and that
of most other AGNs targeted so far for CO measurements. While the large
velocity dispersion of the CO line suggests a post merger system, J0015+1842 is
observed to be a regular, only very moderately dust-reddened (Av~0.3-0.4)
type-I quasar from its UV-optical spectrum, from which we infer a mass of the
super-massive black hole be around M_BH~6x10^8 Msun. We suggest that J0015+1842
is observed at a galaxy evolutionary stage where a massive merger has brought
significant amounts of gas towards an actively accreting super-massive black
hole (quasar) that already cleared the way in the circum-nuclear region towards
the observer through powerful winds, while the host still contains a large
amount of dust and molecular gas with high velocity dispersion. Observations of
a sample of similar systems should help determining better the respective
importance of evolution and orientation in the appearance of quasars and their
host galaxies and have the potential to investigate early feedback and
star-formation processes in galaxies in their quasar phases.
