Spectral-Line Survey at Millimeter and Submillimeter Wavelengths toward an Outflow-Shocked Region, OMC 2-FIR 4

TL;DR

This spectral-line survey at millimeter and submillimeter wavelengths of the outflow-shocked region OMC 2-FIR 4 identified molecular line profiles, distinguished between ambient and outflow-shocked gas, and analyzed chemical compositions to understand outflow chemistry.

Contribution

First spectral-line survey at 82--106 GHz and 335--355 GHz toward OMC 2-FIR 4, revealing molecular line profiles and chemical characteristics of outflow-shocked gas.

Findings

Detected 120 lines of 20 molecular species.

Narrow components trace ambient dense gas; wide components trace outflow and shocked gas.

Chemical composition similar to L1157 B1, indicating outflow-shocked chemistry.

Abstract

We performed the first spectral-line survey at 82--106 GHz and 335--355 GHz toward the outflow-shocked region, OMC 2-FIR 4, the outflow driving source, FIR 3, and the northern outflow lobe, FIR 3N. We detected 120 lines of 20 molecular species. The line profiles are found to be classifiable into two types: one is a single Gaussian component with a narrow ($<$ 3 km s$^{-1}$) width and another is two Gaussian components with narrow and wide ($>$ 3km s$^{-1}$) widths. The narrow components for the most of the lines are detected at all positions, suggesting that they trace the ambient dense gas. For CO, CS, HCN, and HCO$^{+}$, the wide components are detected at all positions, suggesting the outflow origin. The wide components of C$^{34}$S, SO, SiO, H$^{13}$CN, HC$^{15}$N, H$_2^{13}$CO, H$_2$CS, HC$_3$N, and CH$_3$OH are detected only at FIR 4, suggesting the outflow-shocked gas origin. The rotation diagram analysis revealed that the narrow components of C$_2$H and H$^{13}$CO$^+$ show low temperatures of 12.5$\pm$1.4 K, while the wide components show high temperatures of 20--70 K. This supports our interpretation that the wide components trace the outflow and/or outflow-shocked gas. We compared observed molecular abundances relative to H$^{13}$CO$^+$ with those of the outflow-shocked region, L1157 B1, and the hot corino, IRAS 16293-2422. Although we cannot exclude a possibility that the chemical enrichment in FIR 4 is caused by the hot core chemistry, the chemical compositions in FIR 4 are more similar to those in L1157 B1 than those in IRAS 16293-2422.