Speaker: Takashi Nagao (University of Turku, Finland)
Title: The origin of the peculiar extinction and interstellar polarization in reddened supernovae and the dust properties in external galaxies
Abstract: The extinction and interstellar polarization (ISP) in reddened supernovae (SNe) tend to show different properties from those averagely observed in the Milky Way (MW), displaying smaller total-to-selective extinction ratios and polarization maxima at shorter wavelengths. This can be interpreted as their host galaxies contain dust grains whose properties are substantially different from the MW dust (IS dust scenario). Another possible explanation is that this peculiarity is created by the effects of the multiple scatterings of the SN light by circumstellar (CS) dust grains (CS dust scenario). Clarifying the origin of the non-MW-like extinction and ISP is important not only for performing the precise reddening correction but also for understanding the dust properties in the host galaxies of SNe. In this talk, I will quantitatively demonstrate what kinds of peculiar extinction and ISP can be realized by these scenarios with close attention to the difference between different types of SNe, and identify the origin by comparing these theoretical predictions with observed extinction and ISP in reddened SNe. Based on the conclusion on this origin, I will discuss the dust properties in external galaxies beyond MW.