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 multi-system MMS 2 in the Orion Molecular Cloud-3 region, at an angular resolution of 1.59" (about 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" (about 640 au) and 3.0 times 10-4 M, respectively. We also detect an extended structure traced by C 18 O emission associated the circumbinary envelope at scale of 5.70" (about 2240 au) with an estimated gas mass of 1.4 times 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.