• Nozawa, T.
• Takeuchi, T.
• Asano, R.

Abstract

We investigate the evolution of extinction curves in galaxies based on our evolution model of grain size distribution. In this model, we considered various processes: dust formation by SNe II and AGB stars, dust destruction by SN shocks in the interstellar medium (ISM), metal accretion onto the surface of grains, shattering and coagulation. We find that the extinction curve is flat in the earliest stage of galaxy evolution because the grain size distribution is dominated by large (a & 0.1 µ m, where a is the grain radius) grains produced by stars. As the galaxy is enriched with dust, shattering becomes effective to produce a large abundance of small grains (a . 0.01 µ m). Then, the total surface area of grains per grain mass becomes large, and grain growth becomes effective at small grain radii, forming a bump at a ∼ 10-3 -10-2 µ m on the grain size distribution. Consequently, the extinction curve at ultraviolet (UV) wavelengths becomes steep, and a bump at 1/λ ∼ 4.5 µ m-1 (λ : wavelength) on the extinction curve becomes prominent. The galactic age when the extinction curve has the bump is roughly estimated as t ∼ (τSF /Gyr)1/2 Gyr, where τSF is the star formation timescale. Once coagulation becomes effective, the extinction curves become flatter, but the UV extinction remains overproduced when compared with the Milky Way extinction curve. This discrepancy can be resolved by introducing a stronger contribution of coagulation. Thus, an interplay between shattering and coagulation could be important to reproduce the Milky Way extinction curve. We conclude that the extinction curves of galaxies change drastically through the galaxy lifetime because the main dust processes that contribute to the grain size distribution change....

Topics

• impedance spectroscopy
• surface
• grain
• grain size
• forming
• grain growth