Radio Source W49 and Anomalous OH Emission

Abstract

THE radio source W49 has become of increasing interest recently because of its association with regions of strong anomalous OH emission at radio wavelengths1–6. The source is situated in the galactic plane in a direction of high optical obscuration so that information has to be obtained entirely at radio wavelengths. Observations on the continuum have shown the source to be an HII region and in addition spectral line observations at 21 cm wavelength7 and at the 109α hydrogen recombination line at 6 cm (ref. 8) have indicated that the distance is about 14 kiloparsec. A measure of the electron temperature and of the velocity distribution of the ionized gas has also been obtained from the recombination line observations. This communication presents some new high resolution observations obtained with the recently completed 150 ft radio telescope of the Algonquin Radio Observatory at a wavelength of 2.85 cm, supplemented by observations at 9.45 cm. These results when considered in conjunction with laboratory measurements suggest that the anomalous OH emission observed from the source might be explained as the result of the formation of OH in an electronically excited state by a two-body process.