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名稱Title
2021天文年會
國立嘉義大學蘭潭校區
5月21日至23日

論文摘要

Origin of small grains in the circum-galactic medium

[ Poster ]

Hiroyuki Hirashita (ASIAA); Ting-Wen Lan (UCSC)

The circum-galactic medium (CGM) contains a significant amount of dust, which indicates dust ejection from galaxies. Galactic outflows could enrich the circum-galactic medium (CGM) with dust. Our hydrodynamic simulations (Hou et al. 2018; Aoyama et al. 2019) suggest that the dust supplied by galactic outflows is dominated by large grains because it is injected into the CGM by supernova feedback before being heavily processed by shattering. However, the observed reddening in Mg II absorbers, which trace the CGM, indicates a large abundance of small grains (Menard \& Fukugita 2012; Lin \& Hirashita 2020). To clarify the origin of small grains in the CGM, we examine a possible path of small-grain production through shattering of pre-existing large grains in the CGM. For a possible site for shattering, we consider cool clumps with hydrogen number density 0.1 cm$^{-3}$ and gas temperature $10^4$ K, which are shown to exist through observations of Mg II absorbers. We calculate the evolution of grain size distribution, starting from a large-grain-dominated distribution. With an appropriate turbulence model, we find that small-grain production occurs on a time-scale of a few hundreds of Myr, which is comparable to the theoretically expected lifetime of the cool clumps. We also confirm that the reddening becomes significant on the above time-scale. Therefore, we conclude that shattering in the CGM is a probable reason for the observed reddening in the CGM.