We have carried out millimeter interferometric observations of the Orion Molecular Cloud-2 ( OMC-2 ) FIR 3/4 region at an angular resolution of \sim 3 \arcsec - 7 \arcsec with the Nobeyama Millimeter Array ( NMA ) in the H ^ { 13 } CO ^ { + } ( J =1–0 ) , ^ { 12 } CO ( J =1–0 ) , SiO ( v =0 , J =2–1 ) , and CS ( J =2–1 ) lines and in the 3.3 mm continuum emission .
Submillimeter single-dish observations of the same region have also been performed with Atacama Submillimeter Telescope Experiment ( ASTE ) in the ^ { 12 } CO ( J =3–2 ) and CH _ { 3 } OH ( J _ { K } =7 _ { K } –6 _ { K } ) lines .
Our NMA observations in the H ^ { 13 } CO ^ { + } emission have revealed 0.07 pc-scale dense gas associated with FIR 4 .
The ^ { 12 } CO ( J =3–2,1–0 ) emission shows high-velocity blue and red shifted components at the both north-east and south-west of FIR 3 , suggesting a molecular outflow nearly along the plane of the sky driven by FIR 3 .
The SiO ( v =0 , J =2–1 ) and the submillimeter CH _ { 3 } OH ( J _ { K } =7 _ { K } –6 _ { K } ) emission , known as shock tracers , are detected around the interface between the outflow and the dense gas .
Furthermore , the ^ { 12 } CO ( J =1–0 ) emission shows an L-shaped structure in the P-V diagram .
These results imply presence of the shock due to the interaction between the molecular outflow driven by FIR 3 and the dense gas associated with FIR 4 .
Moreover , our high angular-resolution ( \sim 3 \arcsec ) observations of FIR 4 in the 3.3 mm continuum emission with the NMA have first found that FIR 4 consists of eleven dusty cores with a size of \sim 1500 - 4000 AU and a mass of \sim 0.2 - 1.4 M _ { \odot } .
The separation among these cores ( \sim 5 \times 10 ^ { 3 } AU ) is on the same order of the Jeans length ( \sim 13 \times 10 ^ { 3 } AU ) , suggesting that the fragmentation into these cores has been caused by the gravitational instability .
The time scale of the fragmentation ( \sim 3.8 \times 10 ^ { 4 } yr ) , estimated from the separation divided by the sound speed , is similar to the time scale of the interaction between the molecular outflow and the dense gas ( \sim 1.4 \times 10 ^ { 4 } yr ) .
We suggest that the interaction between the molecular outflow from FIR 3 and the dense gas at FIR 4 triggered the fragmentation into these dusty cores , and hence the next generation of the cluster formation in FIR 4 .