Context : Using the IRAM 30m telescope , we have detected the ^ { 12 } 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 H _ { 2 } densities in the range 10 ^ { 3.5 } -10 ^ { 4.0 } cm ^ { -3 } , and kinetic temperatures between 50 K and 200 K. The H _ { 2 } mass of ( 3.6 - 5.4 ) \times 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 \times 10 ^ { 9 } M _ { \sun } , and cold and hot dust temperatures of 42 \pm 5 K and 160 \pm 25 K , respectively .
The broad MgII line allows us to estimate the mass of the central black hole as 1.7 \times 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 .

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Conclusions : Galaxies : evolution – Galaxies : starburst – Galaxies individual ( J100038+020822 ) – Galaxies : ISM – Galaxies : quasars : emission lines – Galaxies : high-redshift