2016ApJ...818..196L

We report the detection of CO(J = 3 -> 2) line emission in the strongly lensed submillimeter galaxy (SMG) SMM J0939+8315 at z = 2.221, using the Combined Array for Research in Millimeter-wave Astronomy. SMM J0939+8315 hosts a type-2 quasar, and is gravitationally lensed by the radio galaxy 3C220.3 and its companion galaxy at z = 0.685. The 104 GHz continuum emission underlying the CO line is detected toward 3C220.3 with an integrated flux density of S_cont= 7.4±1.4 mJy. Using the CO(J = 3 -> 2) line intensity of I_CO(3–2)= (12.6±2.0) Jy km/s, we derive a lensing- and excitation-corrected CO line luminosity of L'_CO(1–0) = (3.4±0.7)x10¹⁰ (10.1/µ_L) K km/s pc² for the SMG, where µ_L is the lensing magnification factor inferred from our lens modeling. This translates to a molecular gas mass of M_gas= (2.7±0.6)x10¹⁰ (10.1/µ_L) M_☉. Fitting spectral energy distribution models to the (sub)-millimeter data of this SMG yields a dust temperature of T = 63.1_–1.3^+1.1 K, a dust mass of M_dust= (5.2±2.1)x10⁸ (10.1/µ_L) M_☉, and a total infrared luminosity of L_IR= (9.1±1.2) x10¹² (10.1/µ_L) L_☉. We find that the properties of the interstellar medium of SMM J0939+8315 overlap with both SMGs and type-2 quasars. Hence, SMM J0939+8315 may be transitioning from a starbursting phase to an unobscured quasar phase as described by the ''evolutionary link'' model, according to which this system may represent an intermediate stage in the evolution of present-day galaxies at an earlier epoch.