Work

An ACA Map of a Molecular Cloud Interacting with Supernova Remnant W28

Year: 2026

Type: article

Abstract: Supernova remnants (SNRs) strongly influence the physical and chemical properties of the molecular clouds (MCs) with which they interact. We carried out a high-resolution observation toward W28F, a chemically rich MC interacting with SNR W28, with the Atacama Compact Array (ACA) in Band 7. Significant emission (>10 σ ) of CO, CH 3 OH, p -H 2 CO, SiO, and SO is detected. We reveal the clumpy structures of the shocked MC, with different spatial distributions between CH 3 OH and SiO. We select six molecular clumps to conduct spectral decomposition and non–local thermodynamic equilibrium analysis with the CH 3 OH and p -H 2 CO lines. The best-fit results show a H 2 density of n H 2 ∼ 1 –3 × 10 5 cm −3 and a gas temperature of T gas ∼ 50–170 K in most of the fitted components. The H 2 density and gas temperature show a clear anticorrelation across different regions, with the thermal pressure consistent with that of the adjacent X-ray-emitting hot plasma. This is consistent with the picture that the SNR shocks propagate into multiphase gas, with a pressure balance existing between different phases. We propose that the high abundance ratio between E-CH 3 OH and A-CH 3 OH (>0.9) suggests extra gas-phase processes to enhance this ratio, such as proton exchange with H 3 + and HCO + . The chemical segregation between CH 3 OH and SiO, in both the spatial and spectral regime, can be explained by the fact that CH 3 OH traces slow shocks while SiO traces fast shocks.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/ae839a