THE DUST BUDGET OF THE SMALL MAGELLANIC CLOUD: ARE ASYMPTOTIC GIANT BRANCH STARS THE PRIMARY DUST SOURCE AT LOW METALLICITY?

Abstract

We estimate the total dust input from the cool evolved stars in the Small\nMagellanic Cloud (SMC), using the 8 micron excess emission as a proxy for the\ndust-production rate. We find that Asymptotic Giant Branch (AGB) and red\nsupergiant (RSG) stars produce (8.6-9.5) x 10^7 solar masses per year of dust,\ndepending on the fraction of far-infrared sources that belong to the evolved\nstar population (with 10%-50% uncertainty in individual dust-production rates).\nRSGs contribute the least (<4%), while carbon-rich AGB stars (especially the\nso-called "extreme" AGB stars) account for 87%-89% of the total dust input from\ncool evolved stars. We also estimate the dust input from hot stars and\nsupernovae (SNe), and find that if SNe produce 10^-3 solar masses of dust each,\nthen the total SN dust input and AGB input are roughly equivalent. We consider\nseveral scenarios of SNe dust production and destruction and find that the\ninterstellar medium (ISM) dust can be accounted for solely by stellar sources\nif all SNe produce dust in the quantities seen around the dustiest examples and\nif most SNe explode in dense regions where much of the ISM dust is shielded\nfrom the shocks. We find that AGB stars contribute only 2.1% of the ISM dust.\nWithout a net positive contribution from SNe to the dust budget, this suggests\nthat dust must grow in the ISM or be formed by another unknown mechanism.\n