Oral Presentation

Evolution of dust grain porosity in galaxies and its influence on extinction curves

Author(s): Hiroyuki Hirashita (ASIAA), Vladimir B. Il'in

Presenter: Hiroyuki Hirashita (ASIAA)

For extragalactic objects, most dust models assume compact grains. However, grains may be porous, which could alter the link between the grain size distribution and the observed dust properties (here we focus on extinction curves). Indeed, coagulation, which our previous dust evolution models have shown to be efficient in Milky Way-like galaxies, could develop porous (or fluffy) grains. In this study, we develop a model for the evolution of size-dependent grain porosity and grain size distribution over the entire history of galaxy evolution. We include stellar dust production, supernova dust destruction, shattering, coagulation, and accretion. Coagulation is assumed to be the source of grain porosity. We use a one-zone model as a first step. We find that porosity develops after small grains are sufficiently created by the interplay between shattering and accretion and are coagulated. The porosity develops around grain radii of 0.03 μm. We also find that the grains are more porous if the ISM is dominated by the diffuse medium because efficient shattering continuously supplies small grains acting as ingredients of porous grains. The porosity steepens the extinction curve significantly for silicate, but not much for carbonaceous dust. We discuss our results in the context of galaxy evolution. In particular, we argue a possibility that diffuse gas in high-redshift galaxies as traced by extended [C II] emission could contribute to producing porous grains, which steepen the extinction curves (leading to efficient extinction of ultraviolet light).