THE ORIGIN OF DUST EXTINCTION CURVES WITH OR WITHOUT THE 2175 Å BUMP IN GALAXIES: THE CASE OF THE MAGELLANIC CLOUDS

Abstract

The Large and Small Magellanic Clouds (LMC and SMC, respectively) are observed to have characteristic dust extinction curves that are quite different from those of the Galaxy (e.g., strength of the 2175 A bump). Although the dust composition and size distribution of the Magellanic Clouds (MCs) that can self-consistently explain their observed extinction curves have been already proposed, it remain unclear whether and how the required dust properties can be achieved in the formation histories of the MCs. We therefore investigate the time evolution of the dust properties of the MCs and thereby derive their extinction curves using one-zone chemical evolution models with formation and evolution of small and large silicate and carbonaceous dust grains and dusty winds associated with starburst events. We find that the observed SMC extinction curve without a conspicuous 2175 A bump can be reproduced well by our SMC model, if the small carbon grains can be selectively lost through the dust wind during the latest starburst about 0.2 Gyr ago. We also find that the LMC extinction curve with a weak 2175 A bump can be reproduced by our LMC model with less efficient removal of dust through dust wind. We discuss possible physical reasons for different dust wind efficiencies between silicate and graphite and among galaxies.