A search for co-evolving ion and neutral gas species in prestellar molecular cloud cores

TL;DR

This study uses coupled chemical and dynamical models to investigate the spatial distribution of ion and neutral gas species in prestellar cores, aiming to identify co-evolving pairs suitable for magnetic field measurements.

Contribution

It introduces a comprehensive modeling approach to assess co-evolution of ion-neutral pairs, proposing new candidate pairs for observational magnetic field studies.

Findings

HCO+/NO, HCO+/CO, and NO+/NO are identified as good co-evolving ion-neutral pairs.

Ion and neutral species may not always trace the same regions, affecting linewidth-based magnetic field estimates.

The models highlight the importance of chemical and dynamical coupling in interpreting spectral line observations.

Abstract

Comparison of linewidths of spectral line profiles of ions and neutral molecules have been recently used to estimate the strength of the magnetic field in turbulent star-forming regions. However, the ion (HCO+) and neutral (HCN) species used in such studies may not be necessarily co-evolving at every scale and density and may thus not trace the same regions. Here, we use coupled chemical/dynamical models of evolving prestellar molecular cloud cores including non-equilibrium chemistry, with and without magnetic fields, to study the spatial distribution of HCO+ and HCN, which have been used in observations of spectral linewidth differences to date. In addition, we seek new ion-neutral pairs that are good candidates for such observations because they have similar evolution and are approximately co-spatial in our models. We identify three such good candidate pairs: HCO+/NO, HCO+/CO, and NO+/NO.