Backscattering and Line Broadening in Orion

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 Alfven waves in conditions where the ratio of magnetic and thermal energies are about equal and constant throughout the ionized gas.

Automated summary

Examination of emission lines in high-resolution optical spectra of the Orion Nebula confirms that the red wing of the main ionization front emission line is caused by backscattering in the Photon Dominated Region. The scattered light component has a weak wavelength dependence, possibly from interstellar medium particles or foreground particles in the Orion Nebula Cluster. An anomalous line-broadening component, known for over 60 years, is characterized in unprecedented detail, and it could be due to turbulence or Alfven waves in ionized gas with equal and constant magnetic and thermal energies.