Molecular clouds under the influence of massive stars in the Galactic HII region G353.2+0.9

TL;DR

This study investigates the physical properties, morphology, and molecular composition of the molecular clouds in the Galactic HII region G353.2+0.9, influenced by the massive star cluster Pismis-24, revealing detailed gas dynamics and chemical variations.

Contribution

It provides a comprehensive analysis of the gas and dust physical parameters and molecular abundances in G353.2+0.9 using multi-line observations and Bayesian non-LTE modeling, highlighting the impact of massive stars.

Findings

Total gas mass ~2000 solar masses

Detection of at least 14 molecular clumps

Temperature and density variations near the ionization front

Abstract

The Galactic HII region G353.2+0.9 is excited by the massive open cluster Pismis-24. By analyzing (sub-)mm molecular-line and -continuum we study the detailed morphology of the gas and dust, as well as their physical parameters and their variation across the PDR. We observed various molecules and transitions to derive the physical properties of the molecular gas through line ratios, and both LTE and non-LTE analyses. The physical properties of the gas were derived with a Bayesian approach for the non-LTE analysis. Based on the continuum data at 870 micron, we derived the dust mass and the column density of H2, and thus the molecular abundances. The total mass of the gas in the region is ca. 2000 Mo, while that of the dust is ca. 21 Mo. A velocity gradient in the region suggests that the expansion of the ionized gas is pushing the molecular gas away from the observer. We unambiguously identify the ionization front, at the location of which we detect an increase in gas density and temperature. We find at least 14 clumps at different positions and LSR velocities. We derive kinetic temperatures in the ranges 11-45 K (CS) and 20-45 K (CN). The H2 number density is typically around 1e5 cm^-3 from CS and few 1e5 cm^-3 from CN, with maxima above 1e6 cm^-3. The abundances of the molecules observed vary across the region, and appear to be higher in regions further away from the ionization front.