Backscattering and Line Broadening in Orion

TL;DR

This study analyzes emission line profiles in the Orion Nebula, confirming backscattering effects and characterizing longstanding line broadening, exploring turbulence and magnetic wave contributions to the observed phenomena.

Contribution

It provides detailed characterization of the anomalous line broadening and confirms backscattering in the Orion Nebula, offering insights into the physical conditions of the region.

Findings

Backscattering causes red wing emission in Orion spectra.

Line broadening is characterized in unprecedented detail.

Possible link between turbulence, magnetic waves, and line broadening.

Abstract

Examination of emission lines in high-velocity resolution optical spectra of the Orion Nebula confirms that the velocity component on the red wing of the main ionization front emission line is due to backscattering in the Photon Dominated Region. This scattered light component has a weak wavelength dependence that is consistent with either general interstellar medium particles or particles in the foreground of the Orion Nebula Cluster. An anomalous line-broadening component that has been known for 60+ years is characterized in unprecedented detail. Although this extra broadening may be due to turbulence along the line-of-sight of our spectra, we explore the possibility that it is due to \alf\ waves in conditions where the ratio of magnetic and thermal energies are about equal and constant throughout the ionized gas.