Properties of extragalactic dust inferred from linear polarimetry of Type Ia Supernovae

Abstract

Aims. The aim of this paper is twofold: 1) to investigate the properties of extragalactic dust and compare them to what is seen in the Galaxy; 2) to address in an independent way the problem of the anomalous extinction curves reported for reddened Type Ia Supernovae (SN) in connection to the environments in which they explode. Methods. The properties of the dust are derived from the wavelength dependence of the continuum polarization observed in four reddened Type Ia SN: 1986G, 2006X, 2008fp, and 2014J. The method is based on the observed fact that Type Ia SN have a negligible intrinsic continuum polarization. This and their large luminosity makes them ideal tools to probe the dust properties in extragalactic environments.Results. All four objects are characterized by exceptionally low total-to-selective absorption ratios (R V ) and display an anomalous interstellar polarization law, characterized by very blue polarization peaks. In all cases the polarization position angle is well aligned with the local spiral structure. While SN 1986G is compatible with the most extreme cases of interstellar polarization known in the Galaxy, SN 2006X, 2008fp, and 2014J show unprecedented behaviours. The observed deviations do not appear to be connected to selection effects related to the relatively large amounts of reddening characterizing the objects in the sample. Conclusions. The dust responsible for the polarization of these four SN is most likely of interstellar nature. The polarization properties can be interpreted in terms of a significantly enhanced abundance of small grains. The anomalous behaviour is apparently associated with the properties of the galactic environment in which the SN explode, rather than with the progenitor system from which they originate. For the extreme case of SN 2014J, we cannot exclude the contribution of light scattered by local material; however, the observed polarization properties require an ad hoc geometrical dust distribution.

NO X-RAYS FROM THE VERY NEARBY TYPE Ia SN 2014J: CONSTRAINTS ON ITS ENVIRONMENT

“…The analysis of the spectra and broadband photometry of SN 2014J by Goobar et al (2014) indicates a local color excess E(B − V ) host ∼ 1.2 mag and a low value of total-toselective extinction R V < 2. These results are consistent with earlier reports by Cox et al (2014) and Patat et al (2014). In the remaining of the paper we follow Goobar et al (2014) and use E(B − V ) host = 1.22 ± 0.05 mag with R host V = 1.40 ± 0.15 mag.…”

On the Time Variation of Dust Extinction and Gas Absorption for Type Ia Supernovae Observed through a Nonuniform Interstellar Medium

“…To account for the "peculiar" dust properties for SNe Ia, it has been suggested that scattered light by dust in a circumstellar medium (CSM) associated with an SN Ia may provide an explanation for both the low values of R V (Wang 2005;Patat et al 2006;Goobar 2008) and λ max (Patat et al 2015;Hoang 2017). Observationally, CSM indeed seems to be present for at least some SNe Ia, as evidenced by the detection of SN-CSM interactions (e.g, Hamuy et al 2003;Aldering et al 2006;Dilday et al 2012), blueshifted and time-varying Na I or K I absorption features (e.g., Patat et al 2007;Simon et al 2009;Fox & Filippenko 2013;Sternberg et al 2014;Graham et al 2015), and the imbalance between the blue-and redshifted Na I absorption components (Sternberg et al 2011;Foley et al 2012;Maguire et al 2013;Phillips et al 2013).…”

“…On the other hand, stringent limits on CSM density has been placed on two of the nearest SNe Ia, SN 2011fe and SN 2014J (e.g., Chomiuk et al 2012;Pérez-Torres et al 2014;Margutti et al 2014;Brown et al 2015;Harris et al 2016;Johansson et al 2017). Indeed, for most SNe Ia, observational evidence points in the direction of interstellar dust being at least the dominant cause for extinction, including those that are highly reddened (e.g., Patat et al 2007;Chotard et al 2011;Phillips et al 2013;Patat et al 2015;Maeda et al 2016;Zelaya et al 2017;Huang et al 2017;Bulla et al 2017). The low values of R V and λ max for some SNe Ia may then be the result of the dust grain size distribution in some of the host galaxies being different from the MW and/or possibly having been altered by SN radiation (e.g., Hoang 2017).…”

A reddening-free method to estimate the56Ni mass of Type Ia supernovae

“…Taking spectroscopic features that correlate with luminosity into account, Chotard et al (2011) found an R V of 2.8 ± 0.3 that is consistent with the Milky Way value. However, objects with high extinction are seen to have an unusually low R V (Phillips et al 2013;Patat et al 2015). Interstellar dust means that a correction for reddening in the Milky Way and the host galaxy needs to be applied.…”