Chemical composition in the IRAS 16562--3959 high-mass star-forming region

TL;DR

This study uses ALMA data to analyze the chemical composition and structure of a high-mass star-forming region, revealing molecular cores, complex organic molecules, and shock-related chemical enhancements.

Contribution

First detailed spatial analysis of molecular cores and chemical composition in IRAS 16562--3959 using high-resolution ALMA data.

Findings

Identification of three molecular cores with distinct chemical signatures

Detection of complex organic molecules in specific cores

Evidence of shock-induced chemical enhancement around the hypercompact HII region

Abstract

We have analyzed the Atacama Large Millimeter/submillimeter Array (ALMA) cycle 2 data of band 6 toward the G345.4938+01.4677 massive young protostellar object (G345.5+1.47 MYSO) in the IRAS 16562--3959 high-mass star-forming region with an angular resolution of $\sim 0.3"$, corresponding to $\sim 760$ au. We spatially resolve the central region which consists of three prominent molecular emission cores. A hypercompact (HC) H$_{\rm {II}}$ region (Core A) and two molecule-rich cores (Core B and Core C) are identified using the moment zero images of the H30$\alpha$ line and a CH$_{3}$OH line, respectively. Various oxygen-bearing complex organic molecules (COMs), such as (CH$_{3}$)$_{2}$CO and CH$_{3}$OCHO, have been detected toward the positions of Core B and Core C, while nitrogen-bearing species, CH$_{3}$CN, HC$_{3}$N and its $^{13}$C isotopologues, have been detected toward all of the cores. We discuss the formation mechanisms of H$_{2}$CO by comparing the spatial distribution of C$^{18}$O with that of H$_{2}$CO. The $^{33}$SO emission, on the other hand, shows a ring-like structure surrounding Core A, and it peaks on the outer edge of the H30$\alpha$ emission region. These results imply that SO is enhanced in a shock produced by the expanding motion of the ionized region.