2014/12/19 by M. Rigault, G. Aldering, M. Kowalski +35 · 1 citation
Physics and Astronomy · #astro-ph.CO
paper · pdf · doi:10.1088/0004-637x/802/1/20
3 Figures ; Submitted to ApJ: Oct.~30, 2014 -- Accepted: Dec.~17, 2014
arxiv created 2014/12/19 · arxiv updated 2019/08/15
Previously we used the Nearby Supernova Factory sample to show that 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. The effect is seen using both the SALT2 and MLCS2k2 lightcurve fitting and standardization methods, with brightness differences of 0.094 ± 0.037 mag for SALT2 and 0.155 ± 0.041 mag for MLCS2k2 with RV=2.5. When combined with our previous measurement the effect is 0.094 ± 0.025 mag for SALT2. If the ratio of these local SN~Ia environments changes with redshift or sample selection, this can lead to a bias in cosmological measurements. 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 HST 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 H0corr=70.6± 2.6 \mathrmkm s-1 Mpc-1 when using the LMC distance, Milky Way parallaxes and the NGC~4258 megamaser as the Cepheid zeropoint, and 68.8± 3.3 \mathrmkm s-1 Mpc-1 when only using NGC~4258. Our correction brings the direct measurement of H0 within ∼ 1 σ of recent indirect measurements based on the CMB power spectrum.