  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
(SdV = 3.1 Jy km/s), behind the nearby merging galaxies VV114 using the Atacama
Large Millimeter/submillimeter Array (ALMA) Band 3. We also find an 880-um
counterpart with ALMA Band 7 (S_880um = 11.2 mJy). A careful comparison of the
intensities of the line and the continuum suggests that the line is a
redshifted 12CO 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_X ~ 10^44 erg/s) active galactic nucleus obscured by a large
hydrogen column (N_H ~ 2 x 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 \ge
1 Jy km/s is ~ 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.

Astrophysics of Galaxies