A survey of recombination line emission from the galactic plane at 325 MHz.

Abstract

A survey of the H272-alpha recombination line at 325 MHz has been made towards 53 directions in the galactic plane using the Ooty Radio Telescope (ORT). Thirty-four of these directions correspond to well-known HII regions, 12 to SNRs and 6 to 'blank' areas selected so that the 5 GHz continuum is a minimum over the telescope beam of 2 deg x 6 arcmin. The observing procedure and spectra of 47 sources towards which lines are detected are presented. Hydrogen recombination lines have been detected towards all the observed directions having l less than 40 deg. Carbon recombination lines are identified in 12 of the directions. The hydrogen line intensities are found to correlate well with the total continuum intensity (which includes the nonthermal galactic background), indicating that most of the lines arise due to stimulated emission by the background radiation. A preliminary discussion on the nature of the line-emitting regions is also presented.