Examining extinction distributions for type Ia supernovae in simulated 3D galaxies

Dust extinction and reddening, commonly parameterized by A_V and E(B-V), respectively, greatly contribute to type Ia supernovae (SNe Ia) observed color and magnitude variations. The models used to describe the extinction probability density function (PDF) are often simplistic and outdated, which can negatively impact SN simulations and cosmology, adding to systematic errors. We present an analysis of simulated SN Ia extinction in galaxies along realistic lines of sight and investigate the parameterization of its PDF p(A_V), as well as its dependence on host properties, such as morphology and dust mass. We employed SKIRT, a radiative transfer code, to simulate observations of SNe Ia in various locations of different galaxies and generate synthetic extinction distributions. To parameterize and fit these distributions, we used both the commonly assumed single-parameter exponential PDF and some of its two-parameter generalizations. We find that the standard exponential PDF does not adequately describe simulated SN extinction: It underestimates low-extinction events and overestimates high-extinction ones. Furthermore, 2D Kolmogorov-Smirnov tests show significant differences between the simulated extinction distributions for SNe in different environments (e.g., bulges or spiral arms), which the exponential parameterization cannot properly distinguish. In contrast, the two-parameter PDFs parameterize SN extinction distributions more accurately across all simulated environments. Variations in host morphology (i.e., SN and dust distributions) or dust mass relate to variations in different PDF parameters, meaning that the two-parameters descriptions offer improved sensibility to host differences. We conclude that the two-parameter Weibull or exponentiated exponential PDFs offer the best overall parameterizations of SN Ia extinction for a wide range of simulated environments. Analyzing observed SN color data from the literature and assuming a Gaussian distribution for the intrinsic component, we conclude that a two-parameter extinction PDF results in SNe being intrinsically redder, with their mean intrinsic color shifted sim2σ in relation to the standard exponential extinction PDF.