Interstellar-Medium Mapping in M82 Through Light Echoes Around Supernova 2014J

TL;DR

This study uses Hubble Space Telescope images to analyze light echoes from supernova 2014J in M82, revealing complex dust structures and grain sizes that influence observed light and extinction.

Contribution

First detailed multi-epoch analysis of supernova light echoes in M82, identifying inhomogeneous dust structures and grain size variations affecting light scattering.

Findings

Detected two main light-echo components with distinct structures.

Found dust grain sizes vary between the diffuse echo and luminous arc.

Suggested the dust causing the luminous arc may also cause supernova extinction.

Abstract

We present multiple-epoch measurements of the size and surface brightness of the light echoes from supernova (SN) 2014J in the nearby starburst galaxy M82. Hubble Space Telescope (HST) ACS/WFC images were taken ~277 and ~416 days after B-band maximum in the filters F475W, F606W, and F775W. Observations with HST WFC3/UVIS images at epochs ~216 and ~365 days (Crotts 2015) are included for a more complete analysis. The images reveal the temporal evolution of at least two major light-echo components. The first one exhibits a filled ring structure with position-angle-dependent intensity. This radially extended, diffuse echo indicates the presence of an inhomogeneous interstellar dust cloud ranging from ~100 pc to ~500 pc in the foreground of the SN. The second echo component appears as an unresolved luminous quarter-circle arc centered on the SN. The wavelength dependence of scattering measured in different dust components suggests that the dust producing the luminous arc favors smaller grain sizes, while that causing the diffuse light echo may have sizes similar to those of the Milky Way dust. Smaller grains can produce an optical depth consistent with that along the supernova-Earth line of sight measured by previous studies around maximum light. Therefore, it is possible that the dust slab, from which the luminous arc arises, is also responsible for most of the extinction towards SN 2014J. The optical depths determined from the Milky Way-like dust in the scattering matters are lower than that produced by the dust slab.