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Abstract:
We present a detailed investigation of millimeter-wave line emitters ALMA J010748.3-173028 (ALMA-J0107a) and ALMA J010747.0-173010 (ALMA-J0107b), which were serendipitously uncovered in the background of the nearby galaxy VV114 with spectral scan observations at λ = 2 - 3 mm. Via Atacama Large Millimeter/submillimeter Array (ALMA) detection of CO(4-3), CO(3-2), and [CI](1-0) lines for both sources, their spectroscopic redshifts are unambiguously determined to be z=2.4666±0.0002 and z=2.3100±0.0002, respectively. We obtain the apparent molecular gas masses Mgas of these two line emitters from [CI] line fluxes as (11.2±3.1)×1010M⊙ and (4.2±1.2)×1010M⊙, respectively. The observed CO(4-3) velocity field of ALMA-J0107a exhibits a clear velocity gradient across the CO disk, and we find that ALMA-J0107a is characterized by an inclined rotating disk with a significant turbulence, that is, a deprojected maximum rotation velocity to velocity dispersion ratio vmax/σv of 1.3±0.3. We find that the dynamical mass of ALMA-J0107a within the CO-emitting disk computed from the derived kinetic parameters, (1.1±0.2)×1010 M⊙, is an order of magnitude smaller than the molecular gas mass derived from dust continuum emission, (3.2±1.6)×1011 M⊙. We suggest this source is magnified by a gravitational lens with a magnification of μ≳10, which is consistent with the measured offset from the empirical correlation between CO-line luminosity and width.