Line Profiles of Cores within Clusters: I. The Anatomy of a Filament

TL;DR

This study uses radiative transfer modeling on hydrodynamic simulations to analyze line profiles of cores within filaments, revealing that infall signatures are often obscured by filamentary structures, affecting observational core-collapse surveys.

Contribution

It demonstrates how filamentary environments influence line profiles of embedded cores, highlighting the limitations of traditional infall indicators in complex molecular cloud structures.

Findings

Optically thick line profiles vary greatly with viewing angle.

Over 50% of angles show no blue asymmetry, challenging traditional infall signatures.

Filament emission can produce red asymmetric profiles, complicating core collapse detection.

Abstract

Observations are revealing the ubiquity of filamentary structures in molecular clouds. As cores are often embedded in filaments, it is important to understand how line profiles from such systems differ from those of isolated cores. We perform radiative transfer calculations on a hydrodynamic simulation of a molecular cloud in order to model line emission from collapsing cores embedded in filaments. We model two optically thick lines, CS(2-1) and HCN(1-0), and one optically thin line, N2H+(1-0), from three embedded cores. In the hydrodynamic simulation, gas self-gravity, turbulence, and bulk flows create filamentary regions within which cores form. Though the filaments have large dispersions, the N2H+(1-0) lines indicate subsonic velocities within the cores. We find that the observed optically thick line profiles of CS(2-1) and HCN(1-0) vary drastically with viewing angle. In over 50% of viewing angles, there is no sign of a blue asymmetry, an idealised signature of infall motions in an isolated spherical collapsing core. Profiles which primarily trace the cores, with little contribution from the surrounding filament, are characterised by a systematically higher HCN(1-0) peak intensity. The N2H+(1-0) lines do not follow this trend. We demonstrate that red asymmetric profiles are also feasible in the optically thick lines, due to emission from the filament or one-sided accretion flows onto the core. We conclude that embedded cores may frequently undergo collapse without showing a blue asymmetric profile, and that observational surveys including filamentary regions may underestimate the number of collapsing cores if based solely on profile shapes of optically thick lines.