TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 65 (No. 10), pp. 1083-1094, 2013

Evolution of dust grain size distribution by shattering in the interstellar medium: Robustness and uncertainty

Hiroyuki Hirashita1 and Hiroshi Kobayashi2

1Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan
2Department of Physics, Nagoya University, Nagoya, Aichi 464-8602, Japan

(Received November 16, 2012; Revised February 27, 2013; Accepted March 9, 2013; Online published October 24, 2013)

Abstract: Shattering of dust grains in the interstellar medium is a viable mechanism of small grain production in galaxies. We examine the robustness or uncertainty in the theoretical predictions of shattering. We identify P1 (the critical pressure above which the deformation destroys the original lattice structures) as the most important quantity in determining the timescale of small grain production, and confirm that the same P1/t (t is the duration of shattering) gives the same grain size distribution [n(a), where a is the grain radius] after shattering within a factor of 3. The uncertainty in the fraction of shocked material that is eventually ejected as fragments causes uncertainties in n(a) by a factor of 1.3 and 1.6 for silicate and carbonaceous dust, respectively. The size distribution of shattered fragments have minor effects as long as αf≤ 3.5 (the size distribution of shattered fragments ∝ af), since the slope of grain size distribution n(a) continuously changes by shattering and becomes consistent with n(a)a-3.5. The grain velocities as a function of grain radius can have an imprint in the grain size distribution especially for carbonaceous dust. We also show that the formulation of shattering can be simplified without losing sufficient precision.
Key words: Cosmic dust, galaxy evolution, grain size distribution, interstellar medium.

Corresponding author E-mail: hirashita@asiaa.sinica.edu.tw

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