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名稱Title
2020天文年會
中研院天文所 國際會議廳

論文摘要

Spectral energy distributions of dust and PAHs based on the evolution of grain size distribution in galaxies

[ Poster ]

Hiroyuki Hirashita (ASIAA); Weining Deng (NTU); Maria S. Murga (Russian Academy of Sciences)

Evolution of infrared dust emission from galaxies has not been understood in a manner consistent with the dust evolution. In this study, we calculate the evolution of infrared spectral energy distribution (SED), considering silicate, carbonaceous dust, and polycyclic aromatic hydrocarbons (PAHs), using our recently developed evolution model of grain size distribution. The dense gas fraction of the interstellar medium (ISM), the star formation time-scale, and the interstellar radiation field intensity are the main parameters. We find that the SED shape generally has weak mid-infrared (MIR) emission in the early phase of galaxy evolution because the dust abundance is dominated by large grains. At an intermediate stage ($\sim$1 Gyr), the MIR emission grows rapidly because the abundance of small grains increases drastically by the accretion of gas-phase metals. We also compare our results with observational data of nearby and high-redshift ($z\sim 2$) galaxies taken by Spitzer. We broadly reproduce the flux ratios in various bands as a function of metallicity. We find that the ISM dominated by the diffuse phase is favored to reproduce the 8 micron intensity dominated by PAHs both for the nearby and the $z\sim 2$ samples. A long star formation time-scale raises the 8 micron emission to a level consistent with the nearby low-metallicity galaxies. The broad match between the theoretical calculations and the observations supports our understanding of the grain size distribution, but the importance of the diffuse ISM for the PAH emission implies the necessity of spatially resolved treatment for the ISM.