The H I emission and absorption spectra towards the double radio source 1830-211

Abstract

The flat-spectrum 1-arcsec double radio source 1830–211 has anomalous spectral and structural properties that do not admit inclusion in any of the known subdivisions of conventional Galactic and extragalactic radio sources. We have observed the H I emission and absorption spectra due to Galactic neutral hydrogen towards the source. A comparison suggests that 1830–211 is extragalactic, consistent with the hypothesis that the source is an example of the gravitational lensing phenomenon. An unusual warm H I component with a spin temperature of about 1000 K has been detected towards the source. This H I fragment is either a peculiar-velocity cloud or else is located beyond the solar circle and about 2 kpc off the Galactic plane.