Infrared properties of OH galaxies

Abstract

The far-infrared (FIR) characteristics of extragalactic OH megamasers and OH absorbers are compared and interpreted. Although both groups require edge-on molecular disk systems, the OH megamasers occur in galaxies with large FIR luminosities L IR and OH absorption in galaxies with lower L IR. The OH luminosity of the observed megamasers varies with L IR , which is in agreement with the predictions of a model for mega-masers having IR-pumped molecular gas amplifying background radio continuum. The proposed pumping scheme relying on the FIR radiation field in the galaxy is generally confirmed. A prediction of the numbers of detectable OH megamasers based on the known properties of megamasers and of luminous FIR sources is in good agreement with the numbers of detected masers. It is more likely to detect a distant luminous maser than a nearby weak one; there is no large detectable population of weak OH megamasers.