Radio Observations of Ionized Hydrogen Nebulæ and Other Discrete Sources at a Wave-length of 9.4 cm.

Abstract

IN recent attempts1–3 to account for the general radio emission from the Galaxy as the integrated radiation of discrete galactic radio sources, it was found necessary to introduce the effect of ionized interstellar hydrogen, H II regions, to fit the observed radio isophotes at various frequencies. Scheuer and Ryle4 detected, at wave-lengths of 1.4 and 3.7 m., a bright band of emission confined within 2° of the galactic equator superimposed on the general radiation. They identified the bright band with thermal emission from a distribution of H II regions. H II regions are strongly concentrated in the galactic plane. The large source, Cygnus X, has been tentatively described as thermal emission5, perhaps from several bright H II regions surrounding γ Cygni5, or from the integrated radiation of all the H II regions in the spiral arm in the direction of Cygnus8. However, Baldwin6 attempted unsuccessfully to detect, at a wave-length of 1.4 m., a very bright individual H II region, the Orion nebula. Observations of discrete sources have been almost entirely confined to metre wave-lengths, where spectra of more than twenty sources have been obtained7. Piddington and Minnett5,8 observed five discrete sources at a wavelength of 25 cm. and the emission at 25 and 10 cm. from a region near the galactic centre. This was an appreciable extension of the short-wave limit of source spectra.