A Sample of Dust Attenuation Laws for DES Supernova Host Galaxies by J. Duarte et al. on Monday 28 November

Type Ia supernovae (SNe Ia) are useful distance indicators in cosmology,

provided their luminosity is standardized by applying empirical corrections

based on light-curve properties. One factor behind these corrections is dust

extinction, accounted for in the color-luminosity relation of the

standardization. This relation is usually assumed to be universal, which could

potentially introduce systematics into the standardization. The ``mass-step''

observed for SNe Ia Hubble residuals has been suggested as one such systematic.

We seek to obtain a completer view of dust attenuation properties for a sample

of 162 SN Ia host galaxies and to probe their link to the ``mass-step''. We

infer attenuation laws towards hosts from both global and local (4 kpc) Dark

Energy Survey photometry and Composite Stellar Population model fits. We

recover a optical depth/attenuation slope relation, best explained by differing

star/dust geometry for different galaxy orientations, which is significantly

different from the optical depth/extinction slope relation observed directly

for SNe. We obtain a large variation of attenuation slopes and confirm these

change with host properties, like stellar mass and age, meaning a universal SN

Ia correction should ideally not be assumed. Analyzing the cosmological

standardization, we find evidence for a ``mass-step'' and a two dimensional

``dust-step'', both more pronounced for red SNe. Although comparable, the two

steps are found no to be completely analogous. We conclude that host galaxy

dust data cannot fully account for the ``mass-step'', using either an

alternative SN standardization with extinction proxied by host attenuation or a

``dust-step'' approach.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.14291v1