The “ \int -shaped filament ” of the Orion A giant molecular cloud was mapped in N _ { 2 } H ^ { + } J = 1 \rightarrow 0 , and its northern end , the OMC-2/3 region was observed also in HC _ { 3 } N J = 5 \rightarrow 4 and CCS J _ { N } = 4 _ { 3 } \rightarrow 3 _ { 2 } and 7 _ { 6 } \rightarrow 6 _ { 5 } .
The results are compared with maps of other molecular lines and the dust continuum emission .
The N _ { 2 } H ^ { + } distribution is similar to the dust continuum distribution , except for the central part of the Orion Nebula .
The distribution of H ^ { 13 } CO ^ { + } holds resemblance to that of dust continuum , but the N _ { 2 } H ^ { + } distribution looks more similar to dust continuum distribution .
The N-bearing molecules , N _ { 2 } H ^ { + } and NH _ { 3 } seem to be more intense in OMC-2 , compared with the H ^ { 13 } CO ^ { + } and CS distribution .
This suggests that OMC-2 has higher abundance of N-bearing molecules or higher filling factor of the quiescent gas .
We identified 34 cloud cores from N _ { 2 } H ^ { + } data .
Their average physical parameters are T _ { ex } = 9.2 \pm 4.2 K , \Delta v = 0.92 \pm 0.52 km s ^ { -1 } , R = 0.086 \pm 0.025 pc , and M = 46 \pm 32 M _ { \odot } .
The masses of cores identified in both N _ { 2 } H ^ { + } and H ^ { 13 } CO ^ { + } in the OMC-2/3 region are rather consistent .
Over the Orion Nebula region , the N _ { 2 } H ^ { + } linewidth is large ( 1.1 - 2.1 km s ^ { -1 } ) .
In the OMC-2/3 region , it becomes moderate ( 0.5 - 1.3 km s ^ { -1 } ) , and it is smaller ( 0.3 - 1.1 km s ^ { -1 } ) in the south of the Orion Nebula .
On the other hand , the gas kinetic temperature of the quiescent cores observed in N _ { 2 } H ^ { + } is rather constant ( \sim 20 K ) over the \int -shaped filament .
The average N _ { 2 } H ^ { + } excitation temperature in Orion cores is \sim 1.6 times as high as that in Taurus cores ( \sim 5.7 K ) .
The N _ { 2 } H ^ { + } excitation temperature decreases toward the south , suggesting the core gas density or N _ { 2 } H ^ { + } abundance decreases toward the south .
We found one peculiar H ^ { 13 } CO ^ { + } core which is not prominent in either N _ { 2 } H ^ { + } , HC _ { 3 } N , or dust .
This core overlaps with the lobe of the intense outflow from a nearby protostar .
We detected no CCS emission in the OMC-2/3 region .
In general , N _ { 2 } H ^ { + } and HC _ { 3 } N distribution is quite similar in the OMC-2/3 region , but we observed displacement between N _ { 2 } H ^ { + } and HC _ { 3 } N over 2 \arcmin scale in OMC-3 , which has a chain of Class 0-I protostars ( candidates ) .
This displacement might be due to either chemical evolution or effect of protostellar outflows .