Investigating the effects of chemistry on molecular line profiles of infalling low mass cores

TL;DR

This study combines chemical, dynamical, and radiative transfer models to analyze molecular line profiles in collapsing low-mass star-forming cores, revealing the impact of freeze-out and temperature gradients on infall signatures.

Contribution

It introduces a coupled modeling approach to predict molecular line profiles considering chemical depletion and dynamical collapse models, highlighting the effects on infall signatures.

Findings

Molecular depletion prevents blue asymmetry in inside-out collapse without temperature gradients.

Extended infall causes blue asymmetry despite late-stage depletion in ambipolar diffusion model.

Inside-out collapse requires temperature gradients and suppressed freeze-out to match observed infall signatures.

Abstract

We have coupled a chemical model with two dynamical models of collapsing low mass star-forming cores to predict abundances across the core of the commonly used infall tracers, CS and HCO$^+$, at various stages of the collapse. The models investigated are a new ambipolar diffusion model and the `inside-out' collapse model. We have then used these results as an input to a radiative transfer model to predict the line profiles of several transitions of these molecules. For the inside-out collapse model, we predict significant molecular depletion due to freeze-out in the core centre, which prevents the formation of the blue asymmetry (believed to be the `signature' of infall) in the line profiles. Molecular depletion also occurs in the ambipolar diffusion model during the late stages of collapse, but the line profiles still exhibit a strong blue asymmetry due to extended infall. For the inside-out collapse model to exhibit the blue asymmetry it is necessary to impose a negative kinetic temperature gradient on the core and suppress freeze-out. Since freeze-out is observed in several class 0 protostars which are thought to be collapsing, this presents a major inconsistency in the inside-out collapse model of star formation.