Millimeter‐ and Submillimeter‐Wave Observations of the OMC‐2/3 Region. I. Dispersing and Rotating Core around the Intermediate‐Mass Protostar MMS 7

We report the results of H13CO+(1-0), CO(1-0), and 3.3 mm dust continuumobservations toward one of the strongest mm-wave sources in OMC-3, MMS 7, withthe Nobeyama Millimeter Array (NMA) and the Nobeyama 45 m telescope. With theNMA, we detected centrally-condensed 3.3 mm dust-continuum emission whichcoincides with the MIR source and the free-free jet. Our combined H13CO+observations have revealed a disk-like envelope. The size and the mass of thedisk-like envelope are 0.15 times 0.11 pc and 5.1 - 9.1 M_sun, respectively.The combined map also shows that the outer portion of the disk-like envelopehas a fan-shaped structure which delineates the rim of the CO(1-0) outflowobserved with the NMA. The position-velocity (P-V) diagrams in the H13CO+ (1-0)emission show that the velocity field in the disk-like envelope is composed ofa dispersing gas motion and a possible rigid-like rotation. The mass dispersingrate is estimated to be (3.4 - 6.0) times 10^-5 M_sun/yr, which implies thatMMS 7 has an ability to disperse ~10 M_sun during the protostellar evolutionaltime of a few times 10^5 yr. The specific angular momentum of the possiblerotation in the disk-like envelope is nearly two orders of magnitude largerthan that in low-mass cores. The turn-over point of the power law of theangular momentum distribution in the disk-like envelope (< 0.007 pc), which islikely to be related to the outer radius of the central mass accretion, issimilar to the size of the 3.3 mm dust condensation. The intermediate-massprotostar MMS 7 is in the last stage of the main accretion phase and that thesubstantial portion of the outer gas has already been dispersed, while the massaccretion may still be on-going at the innermost region traced by the dustycondensation.Comment: 19 pages, 9 figures, ApJ accepted pape