13CO and C 18O J = 2-1 mapping of the environment of the Class 0 protostellar core SMM 3 in Orion B9

Abstract

Context. Observations of molecular spectral lines provide information on the gas kinematics and chemistry of star-forming regions. Aims. We attempt to achieve a better understanding of the gas distribution and velocity field around the deeply embedded Class 0 protostar SMM 3 in the Orion B9 star-forming region. Methods. Using the APEX 12-m telescope, we mapped the line emission from the J = 2-1 rotational transition of two CO isotopologues, 13CO and C 18O, over a 4′ × 4′ region around Orion B9/SMM 3. Results. Both the 13CO and C 18O lines exhibit two well-separated velocity components at about 1.3 and 8.7 km s -1. The emission of both CO isotopologues is more widely distributed than the submillimetre dust continuum emission as probed by LABOCA. The LABOCA 870-μm peak position of SMM 3 is devoid of strong CO isotopologue emission, which is consistent with our earlier detection of strong CO depletion in the source. No signatures of a large-scale outflow were found towards SMM 3. The 13CO and C 18O emission seen at ∼1.3 km s -1 is concentrated into a single clump-like feature at the eastern part of the map. The peak H 2 column density towards a C 18O maximum of the low-velocity component is estimated to be ~10 22 cm -2. A velocity gradient was found across both the 13CO and C 18O maps. Interestingly, SMM 3 lies on the border of this velocity gradient. Conclusions. The 13CO and C 18O emission at ∼1.3 km s -1 is likely to originate from the "low-velocity part" of Orion B. Our analysis suggests that it contains high density gas (∼10 22 H 2 molecules per cm 2), which conforms to our earlier detection of deuterated species at similarly low radial velocities. Higher-resolution observations would be needed to clarify the outflow activity of SMM 3. The sharp velocity gradient in the region might represent a shock front resulting from the feedback from the nearby expanding H ii region NGC 2024. The formation of SMM 3, and possibly of the other members of Orion B9, might have been triggered by this feedback. © ESO, 2012.