Colloquium: Masers and Dense molecular gases in active galactic nuclei

© Yoshiaki Hagiwara

Extragalactic H2O masers have been found in dense gas regions in active galactic nuclei (AGN) and they are known to be a powerful tool for tracing a disc, outflow, or some other kinematics around the active nuclei. I present recent results of ALMA observations of sub-millimeter H2O masers toward the two nearby active galactic nuclei, NGC 4945 and Circinus galaxy, along with single-dish monitoring data of 22 GHz H2O masers.

In addition, the nature of well-known off-nuclear maser in NGC 1068 will be discussed in comparison with existing MERLIN/VLBI/VLA/ALMA data. Molecular lines of HCN and HCO+ have been found at the positions of H2O maser emission, providing information such as velocity fields and physical conditions of the molecular gases, which could help understand a total picture of the nuclear region of the galaxy.