Carbon recombination lines and the neutral hydrogen clouds near the Orion Nebula

Abstract

Both new and previously published observations of carbon recombination lines toward Orion A have been used to construct two-cloud (foreground and background) models for the carbon-line emission. These models indicate that (1) the background carbon-emitting cloud must be nonuniform in electron temperature and/or electron density on a scale near 3 min, (2) the observed intensities of the carbon lines provide useful limits on the range of possible electron density (but not on the range of possible electron temperature) in both carbon-emitting clouds, (3) stimulated emission significantly enhances the intensities of the carbon lines at n greater than or approximately equal to 160, and (4) models which reproduce the observed carbon-line intensities can also reproduce nearly all of the observed carbon-line velocities