Emission and Absorption of Radio Waves in the Galactic Disk

Abstract

Bremsstrahlung in electron collisions with helium atoms produces up to O' 04 % of the radio emission continuum from the main part of interstellar HII regions, while, near the outer edge where hydrogen is about half-ionized, electron collisions with hydrogen atoms produce up to 2% of the normal electron-proton bremsstrahlung. Radio emission and absorption in electron-hydrogen and electron-helium collisions in HI regions are investigated and found to be negligible at the low temperatures therein. However, low energy cosmic rays may ionize HI regions to a sufficient degree to significantly attenuate radio waves by inverse bremsstrahlung (free-free absorption) in electron-proton Coulomb collisions. Future high resolution surveys of the cosmic radio brightness should be able to distinguish between HI and Ell absorption.