date: 2012 February 1 (Wed) 15:00-16:00
room: CPS Conference Room
speaker: Hiroyuki Hirashita (Academia Sinica Institute of Astronomy and Astrophysics)
organizer: Hiroshi Kimura
title: Evolution of grain size distribution in the interstellar medium
abstract: The motion of dust grains in galaxies can be driven by turbulent motion of the interstellar medium (ISM).
It has been suggested that, as a result of gas drag and magnetohyrodynamic resonance, dust grains acquire large velocity dispersions (Yan et al. 2004); in particular, in diffuse ISM, the velocity dispersion becomes so large that when two dust grains encounter, they are shattered into small pieces. In dense ISM, on the other hand, the enhancement of grain velocity dispersions raises the efficiency of grain coagulation (Hirashita and Yan 2009).
Therefore, the interaction between turbulent gas/plasma and dust grains is of fundamental importance in the evolution of grain size distribution in galaxies.

To observationally investigate the modification of the grain size distribution, the extinction curve (wavelength dependence of scattering and absorption of light by dust) is often used.
We have calculated the evolution of extinction curve by taking into account shattering and coagulation driven by interaction between gas/plasma and dust.
In particular, we have found that shattering in warm diffuse medium is efficient enough to modify the extinction curve (Hirashita et al. 2010). We also mention other processes (grain growth, shock destruction, etc.) that could change the extinction curve. Some observations are compared with our theoretical results.
keywords: interstellar dust, grain size distribution, extinction curve, galaxy evolution