A MASSIVE MOLECULAR GAS RESERVOIR IN THE z = 2.221 TYPE-2 QUASAR HOST GALAXY SMM J0939+8315 LENSED BY THE RADIO GALAXY 3C220.3

ABSTRACT 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 Scont = 7.4 1.4 mJy. Using the CO(J = 3 2) line intensity of ICO(3-2) = (12.6 2.0) Jy km s−1, we derive a lensing- and excitation-corrected CO line luminosity of = (3.4 0.7) × 1010 (10.1/ L) K km s−1 pc2 for the SMG, where L is the lensing magnification factor inferred from our lens modeling. This translates to a molecular gas mass of Mgas = (2.7 0.6) × 1010 (10.1/ L) M . Fitting spectral energy distribution models to the (sub)-millimeter data of this SMG yields a dust temperature of T = 63.1 K, a dust mass of Mdust = (5.2 2.1) × 108 (10.1/ L) M , and a total infrared luminosity of LIR = (9.1 1.2) ×1012 (10.1/ 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.