Evolution of grain size distribution in the circumgalactic medium.

This article focuses on modeling the evolution of dust grain size distribution in the circumgalactic medium (CGM) by coupling it with the chemical and dust evolution in the central galaxy, including mass exchange via inflows and outflows. The model incorporates key dust processes in the galaxy—stellar dust production, supernova destruction, shattering, accretion, and coagulation—and in the CGM—sputtering in hot gas and shattering in cool clumps. Results show that the grain size distribution in the CGM generally follows that in the galaxy but is significantly shaped by the balance between sputtering and shattering, with shattering producing small grains that are more susceptible to sputtering. Comparison with observed reddening curves of Mg ii absorbers suggests that efficient inflow from the CGM to the galaxy is necessary to reproduce the observed dust abundance and extinction properties, highlighting the importance of rapid dust and metal enrichment in the CGM. The model provides a theoretical framework useful for interpreting dust-related observations and for incorporation into hydrodynamic simulations of galaxy evolution.