Spectral Survey of the Star Formation Region DR21OH in the 4 mm Wavelength Range

TL;DR

This spectral survey of the DR21OH star formation region in the 4 mm wavelength range identified 69 molecules, including complex organics, revealing new species and demonstrating the effectiveness of spectral line stacking for molecular cloud studies.

Contribution

First comprehensive 4 mm spectral survey of DR21OH detecting a wide range of molecules, including species with no 3 mm transitions, and showcasing spectral line stacking as a powerful method.

Findings

Detected 69 molecules, including complex organics and isotopologues.

Found species with no 3 mm transitions, expanding molecular inventory.

Demonstrated spectral line stacking effectively identifies faint molecules.

Abstract

The results of a spectral survey of the region of massive star formation DR21OH in the 4-mm wavelength range are presented. Sixty-nine molecules and their isotopologues have been detected, ranging from simple diatomic or triatomic species such as SO, SiO and CCH, to complex organic molecules such as CH$_3$OCHO or CH$_3$OCH$_3$. The obtained results qualitatively repeat the results of the survey of the same source at 3~mm. The inventories of molecules found at 3mm and 4mm overlap to a great extent. However, at 4 mm we found a number of species that have no allowed transitions in the 3-mm wavelength range, e.g. DCN, DNC, or SO$^+$. The bulk of the molecules detected at 4~mm are those that are common for dense cores, e.g., HC$_3$N or CH$_3$CCH, but some of the detected species are typical for hot cores. The latter include complex organic molecules CH$_3$OCHO, CH$_3$CH$_2$OH, CH$_3$OCH$_3$, etc. However, the detected emission of these molecules probably arises in a gas heated to 30 K only. Nine molecules, including complex species CH$_3$C$_3$N, CH$_3$CH$_2$CN, CH$_3$COCH$_3$, were found by spectral line stacking. This demonstrates the prospects of the method in the study of molecular clouds.