2006PASJ...58..957I

We present an ∼2'' resolution image of the CO (2-1) emission and an ∼4'' resolution image of the CO (3-2) emission in the z=1.3 hyper-luminous starburst galaxy MIPS J142824.0+352619, obtained at the Nobeyama Radio Observatory. Our new CO (3-2) and CO (2-1) emission detections yield L'_CO(3–2) = 1.4(±0.5) x 10¹¹ and L'_CO(2–1) = 1.2(± 0.3) x 10¹¹ K km s^–1 pc², which translate to a molecular gas mass of ∼10¹¹M_☉, assuming a CO to H₂ conversion factor appropriate for ULIRGs. The derived high CO luminosities place this source as being one of the brightest galaxies detected in CO to date. The CO (3-2) and CO (2-1) derived redshifts are 1.3248±0.0002 and 1.3250±0.0002. If the bulk of the molecular gas traced in these lines is completely thermalized, as suggested by L'_CO(3–2)/L'_CO(2–1) ∼ 1, a constraint to the gas density of n \gtrsim 10³ cm^–3 is obtained from our Large Velocity Gradient (LVG) analysis. If a significant fraction of the bright FIR luminosity of L_FIR = (3.2 ± 0.7) x 10¹³ L_☉ arises from starburst activity, then the Star Formation Efficiency (SFE) is 320 L_☉M_☉^–1. The size constraint of 1".3 given by the CO (2-1) map provides an upper limit to the lensing magnification factor of µ \lesssim 8, which further supports the earlier claim that the magnification of this source is only modest.