Molecular line profiles as diagnostics of protostellar collapse: modelling the `blue asymmetry' in inside-out infall

TL;DR

This study models molecular line profiles in collapsing star-forming cores to understand how line asymmetries, especially blue asymmetry, can serve as indicators of collapse stages, considering chemical and temperature variations.

Contribution

It introduces a chemodynamical model coupling chemistry and radiative transfer to analyze molecular line asymmetries in protostellar collapse, highlighting the impact of temperature and chemical distributions.

Findings

Blue asymmetry correlates with collapse stage in models.

Warm central regions produce higher blue asymmetry.

Line profiles are sensitive to chemical abundance and temperature distributions.

Abstract

The evolution of star-forming core analogues undergoing inside-out collapse is studied with a multi-point chemodynamical model which self-consistently computes the abundance distribution of chemical species in the core. For several collapse periods the output chemistry of infall tracer species such as HCO+, CS, and N2H+, is then coupled to an accelerated Lambda-iteration radiative transfer code, which predicts the emerging molecular line profiles using two different input gas/dust temperature distributions. We investigate the sensitivity of the predicted spectral line profiles and line asymmetry ratios to the core temperature distribution, the time-dependent model chemistry, as well as to ad hoc abundance distributions. The line asymmetry is found to be strongly dependent on the adopted chemical abundance distribution. In general, models with a warm central region show higher values of blue asymmetry in optically thick HCO+ and CS lines than models with a starless core temperature profile. We find that in the formal context of Shu-type inside-out infall, and in the absence of rotation or outflows, the relative blue asymmetry of certain HCO+ and CS transitions is a function of time and, subject to the foregoing caveats, can act as a collapse chronometer. The sensitivity of simulated HCO+ line profiles to linear radial variations, subsonic or supersonic, of the internal turbulence field is investigated in the separate case of static cores.