Circumnuclear water vapor masers in active galaxies

Abstract

VLA observations of the very luminous extragalactic water masers in NGC 4258 and NGC 1068 constrain their spatial extent to less than 1.3 and 3.5 pc respectively at the center of each galaxy. This is evidence that very dense neutral gas is present in the central parsec of these galaxies. The luminous maser emission most likely originates in very dense molecular gas clumps in the immediate vicinity of a central source with mass outflow. The masers could be filamentary structures in the gas near the nuclear object. Results of a survey for water masers in the nuclei of galaxies are also presented.