Masers in AGN environments

TL;DR

This paper reviews the role of maser emissions in active galactic nuclei (AGN), highlighting their use in studying AGN structure and measuring cosmological parameters like the Hubble constant.

Contribution

It emphasizes the significance of H2O masers in AGN for understanding nuclear geometry and deriving precise cosmological measurements, advancing the field's observational techniques.

Findings

H2O masers trace accretion disk structures in AGN

Maser-based measurements improve estimates of the Hubble constant

Masers provide insights into AGN geometry at small scales

Abstract

Galactic nuclei are well known sources of OH and H2O maser emission. It appears that intense star formation in ultra-luminous infrared galaxies drives most OH sources. In contrast, nuclear activity appears to drive most H2O sources. When H2O emission originates in accretion disk structures, constrained geometry and dynamics enable robust interpretation of spectroscopic and imaging data. The principal science includes study of AGN geometry at parsec and sub-parsec radii and measurement of geometric distances in the Hubble Flow. New high accuracy estimates of the Hubble constant, "Ho," obtained from maser distances may enable new substantively improved constraints on fundamental cosmological parameters (e.g., dark energy).