Consistent extinction model for type Ia supernovae in Cepheid-based calibration galaxies and its impact on $H_{0}$

Understand

The most recent SH0ES measurement of the Hubble constant employs corrections of type Ia supernova magnitudes due to extinction in their host galaxies.

• These corrections are estimated using a probabilistic model which is trained on Hubble flow (z>0.03) supernovae and extrapolated to the calibration galaxies (those with observed Cepheids), despite the fact that the latter are selected based on criteria favouring disky and dust-rich systems.
• We show that this standard approach underestimates the brightness of reddened supernovae in the high stellar-mass ($M_{\star}>10^{10}M_{\odot}$) calibration galaxies.
• This can be traced back to the fact that for these galaxies, a low total-to-selective extinction coefficient (R_B~3) is assumed, while for the low stellar-mass analogues a more standard R_ B~4 is adopted.