We report the detection of a distant star-forming galaxy , ALMA J010748.3 - 173028 , which is identified by a 13 \sigma emission line at 99.75 GHz ( S \Delta v = 3.1 Jy km s ^ { -1 } ) , behind the nearby merging galaxies VV114 using the Atacama Large Millimeter/submillimeter Array ( ALMA ) Band 3 .
We also find an 880- \micron counterpart with ALMA Band 7 ( S _ { \mathrm { 880 \mu m } } = 11.2 mJy ) .
A careful comparison of the intensities of the line and the continuum suggests that the line is a redshifted ^ { 12 } CO transition .
A photometric redshift analysis using the infrared to radio data favors a CO redshift of z = 2.467 , although z = 3.622 is acceptable .
We also find a hard X-ray counterpart , suggesting the presence of a luminous ( L _ { \mathrm { X } } \sim 10 ^ { 44 } erg s ^ { -1 } ) active galactic nucleus obscured by a large hydrogen column ( N _ { \mathrm { H } } \sim 2 \times 10 ^ { 23 } cm ^ { -2 } if z = 2.47 ) .
A cosmological simulation shows that the chance detection rate of a CO-emitting galaxy at z > 1 with \geq 1 Jy km s ^ { -1 } is \sim 10 ^ { -3 } per single ALMA field of view and 7.5-GHz bandwidth at 99.75 GHz .
This demonstrates that ALMA has sufficient sensitivity to find an emission-line galaxy such as ALMA J010748.3 - 173028 even by chance , although the likelihood of stumbling across such a source is not high .