We present high resolution imaging of the low order ( J = 1 and 2 ) CO line emission from the z = 3.93 submillimeter galaxy ( SMG ) MM18423+5938 using the Expanded Very Large Array , and optical and near-IR imaging using the Canada-France-Hawaii Telescope .
This SMG with a spectroscopic redshift was thought to be gravitationally lensed given its enormous apparent brightness .
We find that the CO emission is consistent with a complete Einstein ring with a major axis diameter of \sim 1.4 ^ { \prime \prime } , indicative of lensing .
We have also identified the lensing galaxy as a very red elliptical coincident with the geometric center of the ring and estimated its photometric redshift z \sim 1.1 .
A first estimate of the lens magnification factor is m \sim 12 .
The luminosity L ^ { \prime } _ { CO ( 1 - 0 ) } of the CO ( 1 - 0 ) emission is 2.71 \pm 0.38 \times 10 ^ { 11 } ~ { } m ^ { -1 } K km s ^ { -1 } pc ^ { 2 } , and , adopting the commonly used conversion factor for ULIRGs , the molecular gas mass is { { M ( H _ { 2 } ) } } = 2.2 \times 10 ^ { 11 } ~ { } m ^ { -1 } ~ { } { M _ { \odot } } , comparable to unlensed SMGs if corrected by m \sim 12 .
Our revised estimate of the far-IR luminosity of MM18423+5938 is 2 \times 10 ^ { 13 } ~ { } m ^ { -1 } < L _ { FIR } < 3 \times 10 ^ { 14 } ~ { } m ^ { -1 } ~ { } { L _ { \odot } } , comparable to that of ULIRGs .
Further observations are required to quantify the star formation rate in MM18423+5938 and to constrain the mass model of the lens in more detail .