DUST DESTRUCTION RATES AND LIFETIMES IN THE MAGELLANIC CLOUDS

The dust budget in galaxies depends on the rate at which dust grains are created in different stellar sources and destroyed by interstellar shocks. Because of their extensive wavelength coverage, proximity, and nearly face-on geometry, the Magellanic Clouds (MCs) provide a unique opportunity to study these processes in great detail. In this paper, we use the complete sample of supernova remnants (SNRs) in the MCs to calculate the lifetimes and destruction efficiencies of silicate and carbon dust. We find dust lifetimes of 22 13 Myr (30 17 Myr) for silicate (carbon) grains in the LMC, and 54 32 Myr (72 43 Myr) for silicate (carbon) grains in the SMC. The corresponding dust destruction rates are 2.3 x 10-2M yr-1 (5.9 x 10-3M yr-1) and 3.0 x 10-3M yr-1 (5.6 x 10-4M yr-1) for silicate (carbon) grains in the LMC and SMC, respectively. The significantly shorter lifetimes in the MCs, as compared to the Milky Way, are explained as the combined effect of their lower total dust mass and preferentially higher dust-to-gas (D2G) mass ratios in the vicinity of the SNRs. We find that the maximum dust injection rates by asymptotic giant branch stars and core collapse supernovae are an order of magnitude lower than the dust destruction rates by the SNRs, suggesting that most of the dust may be reconstituted in dense molecular clouds. We also discuss the dependence of the dust destruction rate on the local D2G mass ratio, ambient gas density, and metallicity, as well as the application of our results to other galaxies and dust evolution models.