2015 Seminar List:
Luminous 22 GHz water megamaser emission is detected in certain active galaxies of LINER and Sy 2 types, most famously NGC 4258.
In some galaxies, the maser emission appears to originate at sub-parsec scales in a thin, warped accretion disk surrounding the central black hole.
In a subset of such "AGN disk maser" galaxies, the masing accretion disk allows a black hole mass measurement and provides an accurate angular diameter distance to the host galaxy.
The latter yields an independent, direct, and accurate measurement of one key cosmological parameter, the Hubble constant.
The Megamaser Cosmology Project (PI: J. Braatz, NRAO) carries out maser-based observational cosmology and is the first systematic search for and study of nearby AGN disk maser galaxies at ~10 Mpc to 250 Mpc.
I present the results for one galaxy (IC 2560), studied with the VLBA/HSA and the Green Bank Telescope under the Megamaser Cosmology Project.