Variation of Dust Properties with Cosmic Time Implied by Radiative Torque Disruption

Abstract

Dust properties within a galaxy are known to change from the diffuse medium to dense clouds due to increased local gas density. However, the question of whether dust properties change with redshift remains elusive. In this paper, using the fact that the mean radiation intensity of the interstellar medium (ISM) of star-forming galaxies increases with redshift, we show that dust properties should change due to increasing efficiency of rotational disruption by radiative torques, an effect named radiative torque disruption (RATD). We first show that because of RATD, the size distribution of interstellar dust varies with redshift, for instance, dust grains become smaller at higher z . We model the extinction curves and find that the curve becomes steeper with increasing redshift. The ratio of total-to-selective extinction, R V , decreases with redshift and achieves low values of R V  ∼ 1.5–2.5 for grains having a composite structure. We also find that dust properties change with the local gas density because of RATD, but the change is dominated by the radiation field for the diffuse ISM. The low values of R V implied by RATD of interstellar dust could reproduce anomalous dust extinction observed toward supernovae Ia and Small Magellanic Cloud-like extinction curves with a steep far-UV rise toward high- z galaxies. Fluctuations in R V due to interstellar turbulence and varying radiation intensity may resolve the tension in measurements of the Hubble constant using supernovae Ia. We finally discuss the implications of evolving dust properties for high- z astrophysics.