Differences in chemical evolution between isolated and embedded prestellar cores

TL;DR

This study shows that the chemical evolution of prestellar cores is significantly influenced by the density of their surrounding environment, challenging the common assumption of isolated cores in models.

Contribution

It demonstrates the importance of ambient medium density in chemical modeling of prestellar cores, highlighting environmental effects often overlooked.

Findings

Higher ambient density enhances molecular abundances like CO and CS.

Environmental density impacts molecular line profiles and intensities.

Ambient density influences chemical evolution more than initial core equilibrium state.

Abstract

Models of prestellar cores often assume that the cores are isolated from their environment - material outside the core boundary plays no role in the subsequent evolution. This is unlikely to be the case in reality, where cores are located within hierarchically substructured molecular clouds. We investigate the dynamical and chemical evolution of prestellar cores, modelled as Bonnor-Ebert spheres, and show that the density of the ambient medium has a large impact on the resulting chemical properties of the cores. Models embedded in high-density, low-temperature surroundings have greatly enhanced abundances of several molecules, such as CO and CS, compared to models with more diffuse surroundings, corresponding to relatively isolated cores. The predicted intensities and profile shapes of molecular lines are also affected. The density of the ambient medium has a stronger effect on the chemical evolution than whether the cores are initially in or out of equilibrium. This suggests that the impact of environment cannot be neglected when modelling chemistry in prestellar cores; the results of these models are highly sensitive to the assumptions made about the core surroundings.