Extragalactic H₂O masers

Abstract

Twenty-five extragalactic H₂O masers are known, classified as normal masers and megamasers. The first VLBI synthesis images of a normal maser, the one associated with the IC 133 region of M33, as well as observations of its environs, show it to be comparable physically to the most powerful galactic masers. Inference from past observations of megamasers has been that megamasers are intrinsically different than normal masers, arising from uncommon or extreme physical conditions. However, the first ever synthesis images of a megamaser, the one toward the nucleus of NGC 3079, show that this source too is structurally similar to galactic maser sources.