An imaging polarimetry survey of Type Ia supernovae: are peculiar extinction and polarization properties produced by circumstellar or interstellar matter?
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ABSTRACTSome highly reddened Type Ia supernovae (SNeIa) display low total-to-selective extinction ratios (RV 2) in comparison to that of typical Milky Way dust (RV 3.3), and polarization curves that rise steeply to blue wavelengths, with peak polarization values at short wavelengths ($lambda _{ m max} lt 0.4, mu$m) in comparison to the typical Galactic values ($lambda _{ m max} approx 0.55, mu$ m). Understanding the source of these properties could provide insight into the progenitor systems of SNeIa. We aim to determine whether they are the result of the host galaxys interstellar dust or circumstellar dust. This is accomplished by analysing the continuum polarization of 66 SNe Ia in dust-rich spiral galaxies and 13 SNe Ia in dust-poor elliptical galaxies as a function of normalized galactocentric distance. We find that there is a general trend of SNeIa in spiral galaxies displaying increased polarization values when located closer to the host galaxies centre, while SNeIa in elliptical host galaxies display low polarization. Furthermore, all highly polarized SNeIa in spiral host galaxies display polarization curves rising toward blue wavelengths, while no evidence of such polarization properties is shown in elliptical host galaxies. This indicates that the source of the peculiar polarization curves is likely the result of interstellar material as opposed to circumstellar material. The peculiar polarization and extinction properties observed toward some SNe Ia may be explained by the radiative torque disruption mechanism induced by the SN or the interstellar radiation field.
