PROFESSOR LUCAS M. MACRI

Having settled the decades-long bitter debate over the value of the Hubble constant, research on the Extragalactic Distance Scale has seen a remarkable transformation over the past few years. The focus is now on a proper accounting of all sources of systematic uncertainty and the development of new techniques to further increase the accuracy and precision in the measurement of H_0. What is the motivation for further work on the Hubble constant? Measuring H_0 at the percent level will significantly improve the constraints on the equation of state of dark energy and other cosmological parameters from ongoing and planned surveys (such as DES, HETDEX, BigBOSS and LSST). The current uncertainty on H_0 is 3.5% and work is underway to reduce it to 2% or less by mid-2015. A 1% measurement should be achievable by the end of the decade based on Gaia parallaxes and observations with the James Webb Space Telescope. The speaker will review recent progress in the field, including near- and far-infrared observations of Galactic and extragalactic Cepheids, the absolute calibration of the luminosity of type Ia SNe, determinations using baryon acoustic oscillations and the cosmic microwave background, and results based on time-delay distances from strong lensing. He will discuss future prospects using HST, Gaia and JWST.