TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 65 (No. 3), pp. 183-192, 2013

Synthesized grain size distribution in the interstellar medium

Hiroyuki Hirashita1 and Takaya Nozawa2

1Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan
2Kavli Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study, the University of Tokyo, Kashiwa, Chiba 277-8583, Japan

(Received November 7, 2011; Revised March 15, 2012; Accepted March 16, 2012; Online published March 12, 2013)

Abstract: We examine a synthetic way of constructing the grain size distribution in the interstellar medium (ISM). First, we formulate a synthetic grain size distribution composed of three grain size distributions processed with the following mechanisms that govern the grain size distribution in the Milky Way: (i) grain growth by accretion and coagulation in dense clouds, (ii) supernova shock destruction by sputtering in diffuse ISM, and (iii) shattering driven by turbulence in diffuse ISM. Then, we examine if the observational grain size distribution in the Milky Way (called MRN) is successfully synthesized or not. We find that the three components actually synthesize the MRN grain size distribution in the sense that the deficiency of small grains by (i) and (ii) is compensated by the production of small grains by (iii). The fraction of each contribution to the total grain processing of (i), (ii), and (iii) (i.e., the relative importance of the three contributions to all grain processing mechanisms) is 30-50%, 20-40%, and 10-40%, respectively. We also show that the Milky Way extinction curve is reproduced with the synthetic grain size distributions.
Key words: Cosmic dust, interstellar medium, grain size distribution, extinction, Milky Way.

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

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