Low Frequency Carbon Radio Recombination Lines II: The Diffuse Interstellar Medium

Abstract

In the second paper of the series, we have modeled low frequency carbon radio recombination lines (CRRL) from the interstellar medium. Anticipating the LOw Frequency ARray (LOFAR) survey of Galactic CRRLs, we focus our study on the physical conditions of the diffuse cold neutral medium (CNM). We have used the improved departure coefficients computed in the first paper of the series to calculate line-to-continuum ratios. The results show that the line width and integrated optical depths of CRRL are sensitive probes of the electron density, gas temperature, and the emission measure of the cloud. Furthermore, the ratio of CRRL to the [CII] at 158 $\mu$m line is a strong function of the temperature and density of diffuse clouds. Guided by our calculations, we analyze CRRL observations and illustrate their use with data from the literature.

Accepted for publication in ApJ

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Cited by in corpus (15)

• Science with the Murchison Widefield Array: Phase I Results and Phase II Opportunities
• Carbon radio recombination lines from gigahertz to megahertz frequencies towards Orion A
• Mapping low frequency carbon radio recombination lines towards Cassiopeia A at 340, 148, 54 and 43 MHz
• The first detection of radio recombination lines at cosmological distances
• Hunting for the elusive methylene radical
• The ionization fraction in OMC-2 and OMC-3
• Multiline observations of hydrogen, helium, and carbon radio-recombination lines toward Orion A: A detailed dynamical study and direct determination of physical conditions
• Searching for the largest bound atoms in space
• Discovery of Hydrogen Radio Recombination Lines at z=0.89 towards PKS 1830-211
• A High Resolution Study of Carbon Radio Recombination Lines towards Cassiopeia A
• Low-Frequency Radio Recombination Lines Away From the Inner Galactic Plane
• Spectroscopy with the Engineering Development Array: cold H${}^{+}$ at 63 MHz towards the Galactic Centre
• Low-Frequency Carbon Recombination Lines in the Orion Molecular Cloud Complex
• Observations of Carbon Radio Recombination Lines with the NenuFAR telescope. I. Cassiopeia A and Cygnus A
• Constraints on the properties of warm ionized gas from low-frequency hydrogen radio recombination lines