Title:Tension in the Hubble Constant
Abstract:
Currently there is a significant discrepancy between measures of the Hubble constant obtained from modeling Planck observations of the cosmic microwave background, and those from direct local measurements. I will describe new results from a decade-long project to measure the Hubble constant to higher precision and accuracy, the Carnegie-Chicago Hubble Program. This program utilizes the resolution of the Hubble Space Telescope, the long-wavelength reach of Spitzer, the capability of ground-based telescope with a range of aperture sizes, including automated follow-up telescopes, to provide new and independent data for the measurement of extragalactic distances. The CCHP project was initiated in anticipation of the launch of ESA's Gaia satellite. The goal of the program is to reduce systematic errors in the distance scale. A robust determination of the overall systematic uncertainties in Ho can only be achieved using several independent methods. This program includes Cepheids and tip of the red giant branch (TRGB) stars, and Type Ia supernovae, the latter as part of the Carnegie Supernova Project (CSP). For the first time ever, we have an approach as accurate as the Cepheids for the calibration of the extragalactic distance scale.