  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. Using the APEX 12-m telescope, we mapped the line
emission from the J=2-1 rotational transition of two CO isotopologues, 13CO and
C18O, over a 4' x 4' region around Orion B9/SMM 3. Both the 13CO and C18O lines
exhibit two well separated velocity components at about 1.3 and 8.7 km/s. The
emission of both CO isotopologues is more widely distributed than the
submillimetre dust continuum emission as probed by LABOCA. The LABOCA
870-micron 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 C18O emission seen at ~1.3 km/s is concentrated into a single
clump-like feature at the eastern part of the map. The peak H2 column density
towards a C18O maximum of the low-velocity component is estimated to be ~10^22
cm-2. A velocity gradient was found across both the 13CO and C18O maps.
Interestingly, SMM 3 lies on the border of this velocity gradient. The 13CO and
C18O emission at ~1.3 km/s is likely to originate from the "low-velocity part"
of Orion B. Our analysis suggests that it contains high density gas, which
conforms to our earlier detection of deuterated species at similarly low radial
velocities. The sharp velocity gradient in the region might represent a shock
front resulting from the feedback from the nearby expanding HII region NGC
2024. The formation of SMM 3, and possibly of the other members of Orion B9,
might have been triggered by this feedback.
