Nobeyama 45 m mapping observations toward Orion A. III. Multi-line observations toward an outflow-shocked region, Orion Molecular Cloud 2 FIR 4. (20th March 2019)

• Record Type: Journal Article
• Authors: Nakamura, Fumitaka; Oyamada, Shuri; Okumura, Sachiko; Ishii, Shun; Shimajiri, Yoshito; Tanabe, Yoshihiro; Tsukagoshi, Takashi; Kawabe, Ryohei; Momose, Mumetake; Urasawa, Yumiko; Nishi, Ryoichi; Lin, Sheng-Jun; Lai, Shih-Ping; Dobashi, Kazuhito; Shimoikura, Tomomi; Sugitani, Koji
• Is Part Of: Publications of the Astronomical Society of Japan. Volume 71:Supplement 1(2019:Dec.)
• Publication Date: 2019-03-20
• Subjects: ISM: clouds -- ISM: kinematics and dynamics -- ISM: molecules -- ISM: structure -- stars: formation; Astronomy -- Periodicals; 520.5
• DOI: 10.1093/pasj/psz001
• Languages: English
• ISSNs: 0004-6264

Abstract

Abstract: We present the results of mapping observations toward an outflow-shocked region, OMC-2 FIR 4, using the Nobeyama 45 m telescope. We observed the area in 13 CO ( J = 1–0), C 18 O ( J = 1–0), N2 H + ( J = 1–0), CCS ( JN = 87 –76 ), HCO + ( J = 1–0), H 13 CO + ( J = 1–0), HN 13 C ( J = 1–0), H 13 CN ( J = 1–0), DNC ( J = 1–0), N2 D + ( J = 1–0), and DC3 N ( J = 9–8). We detected a dense molecular clump that contains FIR 4/5. We also detected, in the 13 CO line, blueshifted and redshifted components driven presumably by protostellar outflows in this region. The axes of the FIR 3 and VLA 13 outflows, projected on the plane of the sky, appear to point to the FIR 4 clump, suggesting that it may be compressed by protostellar outflows from Class I sources, FIR 3 and VLA 13. Applying a hyperfine fit of N2 H + lines, we estimated the excitation temperature to be ∼20 K. The high excitation temperature is consistent with the fact that the clump contains protostars. CCS emission was detected in this region for the first time. Its abundance is estimated to be a few × 10 −12, indicating that the region is chemically evolved at ∼10 5 yr, which is comparable to the typical lifetime of Class I protostars. This timescale is consistent with the scenario that star formation in FIR 4 is triggered by dynamical compression of the protostellar outflows. The [HNC]/[HCN] ratio was evaluated to be ∼0.5 in the dense clump and the outflow lobes, whereas it is somewhat larger in the envelope of the dense clump. The small [HNC]/[HCN] ratio indicates that HNC formation was prevented due to high temperatures. Such high temperatures seem to be consistent with the scenario that either protostellar radiation, or outflow compression, or both affected the thermal properties of this region.