The Dense Gas Structures around MMS 2/OMC-3 Traced by C 18 O Emission

We report the Atacama Large Millimeter/submillimeter Array observations of 1.3 mm continuum, C 18 O ( J = 2−1), and N 2 D + ( J = 3−2) toward the millimeter multisystem MMS 2 in the Orion molecular cloud 3 region at an angular resolution of 1 . ″ 59 (∼620 au). MMS 2 is in the flat-spectrum phase, with its protostars in the late stage of the main accretion phase. We detect the centrally condensed structures traced by C 18 O emission associated with the 1.3 mm continuum sources MMS 2-North and MMS 2-South, which are spatially resolved and unresolved, respectively. The estimated diameter and mass of the centrally condensed structure associated with MMS 2-North are 1 . ″ 64 (∼640 au) and 3.0 × 10 −4 M ⊙ , respectively. We also detect an extended structure traced by C 18 O emission associated with the circumbinary envelope at a scale of 5 . ″ 70 (∼2240 au) with an estimated gas mass of 1.4 × 10 −2 M ⊙ . In addition, we detect a filamentary structure traced by N 2 D + emission to the south of MMS 2, which is spatially offset from the C 18 O emission. This offset may be attributed to the influence of the warm surrounding environment.