On the evolution of the molecular line profiles induced by the propagation of C-shock waves

TL;DR

This paper models how molecular line profiles evolve during C-shock wave propagation, revealing that narrow SiO emissions in early shock stages are signatures of magnetic precursors, and explains observed velocity components as different shock stages.

Contribution

It introduces a coupled parametric and radiative transfer model to predict molecular line profile variations during C-shock evolution, highlighting the role of magnetic precursors.

Findings

Narrow SiO emission indicates early C-shock magnetic precursors.

Different shock stages coexist, explaining multiple velocity components.

Model matches observed SiO and ion enhancements in young shocks.

Abstract

We present the first results of the expected variations of the molecular line emission arising from material recently affected by C-shocks (shock precursors). Our parametric model of the structure of C-shocks has been coupled with a radiative transfer code to calculate the molecular excitation and line profiles of shock tracers such as SiO, and of ion and neutral molecules such as H13CO+ and HN13C, as the shock propagates through the unperturbed medium. Our results show that the SiO emission arising from the early stage of the magnetic precursor typically has very narrow line profiles slightly shifted in velocity with respect to the ambient cloud. This narrow emission is generated in the region where the bulk of the ion fluid has already slipped to larger velocities in the precursor as observed toward the young L1448-mm outflow. This strongly suggests that the detection of narrow SiO emission and of an ion enhancement in young shocks, is produced by the magnetic precursor of C-shocks. In addition, our model shows that the different velocity components observed toward this outflow can be explained by the coexistence of different shocks at different evolutionary stages, within the same beam of the single-dish observations.