A Search for Recombination Line Emission from the Galactic Equator at 408 MHz

Abstract

A search for H 2520( recombination line emission was made by scanning the galactic equator region using the Molonglo radio telescope. Upper limits were established over the range of galactic longitude accessible to the instrument. For the region III ;S 40°, estimates of the background thermal continuum brightness temperature were used to derive lower limits of ~ 2000 K for the electron temperature of the gas along the line of sight. Lower limits for the electron density obtained by considering probable non-LTE effects suggest that the thermal emission over this range is due to low surface brightness HII regions. The observed H 2520( upper limit averaged over the range 270° ;S I ;S 320° just admits the line intensity calculated by Shaver (1975) for the cold cloud component of the general interstellar medium.

A SURVEY OF RADIO RECOMBINATION LINES USING THE OOTY RADIO TELESCOPE AT 328 MHz IN THE INNER GALAXY

“…Following this many researchers (Lilley et al 1966;Goldberg & Dupree 1967;Gottesman & Gordon 1970;) detected RLs. Subsequent attempts (Batty 1976) to detect RRL at lower frequencies(< 500MHz) seem (Anantharamaiah 1985)to have failed due to non availiability/development of radio telescope hardware. It was already known (Shaver 1975) in the community that stimulated emission(kT /hν× spontaneous) would boost RRL at lower frequencies.…”