2011ApJ...730..108R

We report the detection of luminous CO(J = 2 ⟶ 1), CO(J = 3 ⟶ 2), and CO(J = 4 ⟶ 3) emission in the strongly lensed high-redshift quasars B1938+666 (z = 2.059), HE 0230-2130 (z = 2.166), HE 1104-1805 (z = 2.322), and B1359+154 (z = 3.240), using the Combined Array for Research in Millimeter-wave Astronomy. B1938+666 was identified in a "blind" CO redshift search, demonstrating the feasibility of such investigations with millimeter interferometers. These galaxies are lensing-amplified by factors of µ_L≃ 11-170, and thus allow us to probe the molecular gas in intrinsically fainter galaxies than currently possible without the aid of gravitational lensing. We report lensing-corrected intrinsic CO line luminosities of L'_CO= 0.65-21x10⁹ K km/s pc², translating to H₂ masses of M(H₂) = 0.52-17x10⁹ (α_CO/0.8) M_☉. To investigate whether or not the active galactic nucleus (AGN) in luminous quasars substantially contributes to L_FIR, we study the L'_CO-L _FIR relation for quasars relative to galaxies without a luminous AGN as a function of redshift. We find no substantial differences between submillimeter galaxies and high-z quasars, but marginal evidence for an excess in L_FIR in nearby low-L_FIR AGN galaxies. This may suggest that an AGN contribution to L_FIR is significant in systems with relatively low gas and dust content, but only minor in the most far-infrared-luminous galaxies (in which L_FIR is dominated by star formation).