C. Buton

Abstract: 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 $0.094 \pm 0.037\ \mathrm{mag}$ for SALT2 and $0.155 \pm 0.041\ \mathrm{mag}$ for MLCS2k2 with $R_V=2.5$. When combined with our previous measurement the effect is $0.094 \pm 0.025\ \mathrm{mag}$ 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 $H_0$. \GALEX{} observations show that the SNe~Ia having standardized absolute magnitudes calibrated via the Cepheid period--luminosity relation using {\textit{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 $H_0$ measurement using SNe~Ia is currently overestimated. Correcting for this bias, we find a value of $H_0^{corr}=70.6\pm 2.6\ \mathrm{km\ s^{-1}\ Mpc^{-1}}$ when using the LMC distance, Milky Way parallaxes and the NGC~4258 megamaser as the Cepheid zeropoint, and $68.8\pm 3.3\ \mathrm{km\ s^{-1}\ Mpc^{-1}}$ when only using NGC~4258. Our correction brings the direct measurement of $H_0$ within $\sim 1\,\sigma$ of recent indirect measurements based on the CMB power spectrum.

TL;DR: In this paper, a new method was proposed to standardize type Ia supernova luminosities using flux ratios from a single flux-calibrated spectrum per supernova.

TL;DR: In this article, a series of new models of SN Ia spectral time series that capture a greater amount of supernova diversity than is possible with the models that are currently customary are presented.

TL;DR: Leget et al. as discussed by the authors developed a spectral energy distribution (SED) model, called the SUpernova Generator And Reconstructor (SUGAR), which improves the spectral description of SNe Ia, and consequently could improve the distance measurements.

TL;DR: Huang et al. as mentioned in this paper studied the dust foreground to the highly reddened SN 2012cu, which is projected onto a dust lane in the galaxy NGC 4772, and found the foreground dust-extinction properties for SN2012cu to be consistent with those of the Milky Way.