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

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 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−1, we derive a lensing- and excitation-corrected CO line luminosity of L CO(1-0) ′ ?> = (3.4 ± 0.7) × 1010 (10.1/μ L) K km s−1 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) × 1010 (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) × 108 (10.1/μ L) M ⊙, and a total infrared luminosity of L IR = (9.1 ± 1.2) ×1012 (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.