  Using the IRAM 30m telescope, we have detected the CO J=2-1, 4-3, 5-4, and
6-5 emission lines in the millimeter-bright, blank-field selected AGN COSMOS
J100038+020822 at redshift z=1.8275. The sub-local thermodynamic equilibrium
(LTE) excitation of the J=4 level implies that the gas is less excited than
that in typical nearby starburst galaxies such as NGC253, and in the
high-redshift quasars studied to date, such as J1148+5251 or BR1202-0725. Large
velocity gradient (LVG) modeling of the CO line spectral energy distribution
(CO SED; flux density vs. rotational quantum number) yields H2 densities in the
range 10^{3.5}--10^{4.0} cm-3, and kinetic temperatures between 50 K and 200 K.
The H2 mass of (3.6 - 5.4) x 10^{10} M_sun implied by the line intensities
compares well with our estimate of the dynamical mass within the inner 1.5 kpc
of the object. Fitting a two-component gray body spectrum, we find a dust mass
of 1.2 x 10^{9} M_sun, and cold and hot dust temperatures of 42+/-5 K and
160+/-25 K, respectively. The broad MgII line allows us to estimate the mass of
the central black hole as 1.7 x 10^{9} M_sun. Although the optical spectrum and
multi-wavelength SED matches those of an average QSO, the molecular gas content
and dust properties resemble those of known submillimeter galaxies (SMGs). The
optical morphology of this source shows tidal tails that suggest a recent
interaction or merger. Since it shares properties of both starburst and AGN,
this object appears to be in a transition from a strongly starforming
submillimeter galaxy to a QSO.
