Institute for Advanced Study Astrophysics Seminar

Accurate measurements of H0 - the current expansion rate of the Universe, provide critical independent constraints on dark energy, spatial curvature of the Universe, neutrino physics, and validity of general relativity. The recent Planck results highlight the necessity of an independent determination of H0 at high accuracy. The Mega-maser Cosmology Project (MCP) aims to determine the Hubble Constant at high accuracy by measuring the angular-diameter distance to galaxies in the Hubble Flow. The MCP has been observing ~10 mega-maser disks in Sy2 galaxies suitable for such distance determination. A geometric distance measurement to NGC 6264, a galaxy at 140 Mpc, via micro-arc-second astrometry of its circum-nuclear mega-maser disk, has been demonstrated. The current status of the MCP measurements of H0, and future prospects, will be described. The MCP also provides accurate determination of the central black-hole mass in mega-maser galaxies. The large intrinsic scatter of BH masses in a narrow range of the velocity dispersion of the mega-maser galaxy bulges adds to the observational richness of the well-known M-sigma relation of BH mass and the spherical component of galaxies. The relationship of the thin Keplerian accretion disks delineated by the mega-masers with the obscuring material of the AGN will be briefly discussed. An update on ALMA will also be given.