Survey of OH Masers at 1665 and 1667 MHz. I. Galactic Longitudes 326° to 40°

Abstract

The galactic plane between longitudes 3260 and 3400 has been searched for OH emiSSIOn and bsorption on the 1665 and 1667 MHz transitions. Forty main-line emission sources were detected (27 new ones, 13 previously known), and these constitute a sample complete to a weIl-defined lower intensity limit in this region of sky. Line profiles of all sources are shown and the statistics on variability and on the intensity ratios of the ground state transitions are summarized. The completeness of the sample encouraged us to make a first attempt to construct a luminosity function and to estimate the total number of such masers in our Galaxy. A study of the velocity structures showed these to be extremely varied, but none exceed a total range of 25 km s -1; combined velocity and polarization data are compatible with a Zeeman splitting origin for the circular polarization, and with this interpretation several sources yield an estimate for the line-of-sight magnetic field strength of a few mG. Preliminary investigations of the associations with other celestial objects indicate that many of the masers are loosely associated with HII region complexes, but in at least eight instances no HII regions have yet been detected; of these eight masers, two may be associated with supernova remnants and one with an unidentified nonthermal radio source.