Selected Publications

Previously we used the Nearby Supernova Factory sample to show that Type Ia supernovae (SNe Ia) having locally star-forming environments are dimmer than SNe Ia having locally passive environments. Here we use the Constitution sample together with host galaxy data from GALEX to independently confirm that result. We explore this issue further, using as an example the direct measurement of H0. GALEX observations show that the SNe Ia having standardized absolute magnitudes calibrated via the Cepheid period-luminosity relation using the Hubble Space Telescope originate in predominately star-forming environments, whereas only ~50% of the Hubble-flow comparison sample have locally star-forming environments. As a consequence, the H0 measurement using SNe Ia is currently overestimated. Correcting for this bias, we find a value of H0{corr}= 70.6 ± 2.6 km s-1 Mpc-1 when using the LMC distance, Milky Way parallaxes, and the NGC 4258 megamaser as the Cepheid zero point, and 68.8 ± 3.3 km s-1 Mpc-1 when only using NGC 4258. Our correction brings the direct measurement of H 0 within ~1 σ of recent indirect measurements based on the cosmic microwave background power spectrum.
In ApJ, 2015.