Molecular Line Profiles from a Core Forming in a Turbulent Cloud

TL;DR

This study models molecular line profiles in a forming dense core within a turbulent, magnetized molecular cloud, revealing how velocity and chemical structures influence observable spectral asymmetries during core evolution.

Contribution

It provides a detailed simulation of molecular line profiles considering turbulence, magnetic fields, and chemical depletion, offering new insights into interpreting core dynamics from spectral observations.

Findings

Line profile asymmetries can switch from blue to red during core evolution.

Outer region motions significantly influence observed line profiles.

Red asymmetries may indicate outward motions in turbulent environments.

Abstract

We calculate the evolution of molecular line profiles of HCO$^+$ and C$^{18}$O toward a dense core thatis forming inside a magnetized turbulent molecular cloud. Features of the profiles can be affected more significantly by coupled velocity and abundance structures in the outer region than those in the inner dense part of the core. The velocity structure at large radii is dominated by a turbulent flow nearby and accretion shocks onto the core, which resulting in the variation between inward and outward motions during the evolution of the core. The chemical abundance structure is significantly affected by the depletion of molecules in the central region with high density and low temperature. During the evolution of the core, the asymmetry of line profiles easily changes from blue to red, and vice versa. According to our study, the observed reversed (red) asymmetry toward some starless cores could be interpreted as an intrinsic result of outward motion in the outer region of a dense core, which is embedded in a turbulent environment and still grows in density at the center.