ALMA Observations of the IRDC Clump G34.43+00.24 MM3: Complex Organic and Deuterated Molecules

TL;DR

This study uses ALMA to observe complex organic and deuterated molecules in an IRDC clump, revealing insights into the chemical composition and physical conditions of high-mass star-forming regions.

Contribution

First detection of multiple COMs and deuterated molecules in G34.43+00.24 MM3 HC, showing similarities to high-mass hot cores and indicating a long cold phase.

Findings

COMs are not produced in shocks.

COM abundance similar to high-mass hot cores.

High D2CO/CH3OH ratio suggests a long cold phase.

Abstract

We have observed complex organic molecules (COMs) and deuterated species toward a hot core/corino (HC) associated with the infrared dark cloud (IRDC) clump G34.43+00.24 MM3 with the Atacama Large Millimeter/submillimeter Array (ALMA). We have detected six normal-COMs (CH3OH, CH3CHO, CH3CH2CN, CH3OCH3, HCOOCH3, and NH2CHO), one deuterated-COM (CH2DCN), and two deuterated fundamental molecules (D2CO and DNC) toward G34.43+00.24 MM3 HC. None of these lines, except for CH3OH, are detected toward the shocked regions in our data, which suggests that COMs do not originate in shocks. The abundance of the COMs relative to CH3OH in G34.43+00.24 MM3 HC is found to be similar to those in high-mass hot cores, rather than those in hot corinos in low-mass star-forming regions. This result suggests that the physical conditions of the warm-up phase of G34.43+00.24 MM3 HC are similar to those of high-mass sources. On the other hand, the D2CO abundance relative to CH$_3$OH in G34.43+00.24 MM3 HC is higher than that of other hot cores, and seems to be comparable to that of hot corinos. The relatively high D2CO/CH3OH ratio of G34.43+00.24 MM3 HC implies a long cold starless phase of G34.43+00.24 MM3 HC.