Chemical evolution of cold dark clouds in the vicinity of supernova remnants

TL;DR

This study investigates how supernova-induced increases in cosmic rays and x-ray fluxes alter the chemical composition and evolution of nearby dense molecular clouds over thousands of years.

Contribution

It provides a detailed analysis of chemical and thermal evolution in molecular clouds affected by supernova explosions, highlighting the timescales for reaching chemical equilibrium.

Findings

H atom abundance reaches equilibrium in ~3x10^4 years.

Icy mantle species' abundances respond over 10^4-10^5 years.

Neutral and grain mantle species may not reach equilibrium near middle-aged supernova remnants.

Abstract

The supernova explosion increases cosmic ray and x-ray fluxes in the surrounding interstellar medium. Cosmic ray particles and x-ray radiation penetrate nearby molecular clouds and affect the chemical and thermal evolution of the gas. Here we study chemical changes in the dense molecular gas influenced by a sudden increase of the ionization rate that may be caused by the supernova explosion. At the cloud core density $2 \times 10^4$ cm$^{-3}$, the H atom abundance reaches the equilibrium value at about $3 \times 10^4$ yr after the change in irradiation conditions. The response time of abundances of icy mantle species is $10^4-10^5$ yr. The abundances of neutral and grain mantle species may not reach their equilibrium values in molecular clouds in the vicinity of 'middle-aged' supernova remnants.