Physical Sciences and Mathematics Commons^™

Megamaser Disks In Active Galactic Nuclei, John F. Kartje, Arieh Königl, Moshe Elitzur

Physics and Astronomy Faculty Publications

Recent spectroscopic and VLBI-imaging observations of bright extragalactic H₂O maser sources have revealed that the megamaser emission often originates in thin circumnuclear disks near the centers of active galactic nuclei (AGNs). Using general radiative and kinematic considerations and taking account of the observed flux variability, we argue that the maser emission regions are clumpy, a conclusion that is independent of the detailed mechanism (X-ray heating, shocks, etc.) driving the collisionally pumped masers. We examine scenarios in which the clumps represent discrete gas condensations (i.e., clouds) and do not merely correspond to velocity irregularities in the disk. We show …