Extinction curves flattened by reverse shocks in supernovae

TL;DR

This paper models how reverse shocks in supernovae affect dust extinction curves in young high-redshift galaxies, showing that ambient gas density influences the flatness of these curves and their observational implications.

Contribution

It provides a theoretical analysis of how reverse shock destruction in supernovae shapes dust extinction curves at high redshift, highlighting the role of ambient density.

Findings

Reverse shocks flatten the extinction curves in high-density environments.

High ambient density (n_H > 1 cm^{-3}) produces too flat curves compared to observations.

Dust from supernovae can still explain observed extinction at z~6 despite destruction effects.

Abstract

We investigate the extinction curves of young galaxies in which dust is supplied from Type II supernovae (SNe II) and/or pair instability supernovae (PISNe). Since at high redshift (z>5), low-mass stars cannot be dominant sources for dust grains, SNe II and PISNe, whose progenitors are massive stars with short lifetimes, should govern the dust production. Here, we theoretically investigate the extinction curves of dust produced by SNe II and PISNe, taking into account reverse shock destruction induced by collision with ambient interstellar medium. We find that the extinction curve is sensitive to the ambient gas density around a SN, since the efficiency of reverse shock destruction strongly depends on it. The destruction is particularly efficient for small-sized grains, leading to a flat extinction curve in the optical and ultraviolet wavelengths. Such a large ambient density as n_H > 1 cm^{-3} produces too flat an extinction curve to be consistent with the observed extinction curve for SDSS J104845.05+463718.3 at z=6.2. Although the extinction curve is highly sensitive to the ambient density, the hypothesis that the dust is predominantly formed by SNe at z~6 is still allowed by the current observational constraints. For further quantification, the ambient density should be obtained by some other methods. Finally we also discuss the importance of our results for observations of high-z galaxies, stressing a possibility of flat extinction curves.