The Dust Budget of the SMC: Are AGB Stars the Primary Dust Source at Low Metallicity?

TL;DR

This study estimates the dust contribution of evolved stars in the Small Magellanic Cloud, finding AGB stars as the primary dust source at low metallicity, but suggesting additional mechanisms are needed to explain the total dust budget.

Contribution

It provides a detailed quantification of dust input from AGB stars, RSGs, SNe, and hot stars in the SMC, highlighting the dominant role of carbon-rich AGB stars and the potential need for dust growth in the ISM.

Findings

AGB stars contribute 87%-89% of dust from cool evolved stars.

Total dust input from SNe and AGB stars are roughly equal under certain assumptions.

AGB stars contribute only 2.1% of the ISM dust, implying other processes are involved.

Abstract

We estimate the total dust input from the cool evolved stars in the Small Magellanic Cloud (SMC), using the 8 micron excess emission as a proxy for the dust-production rate. We find that Asymptotic Giant Branch (AGB) and red supergiant (RSG) stars produce (8.6-9.5) x 10^7 solar masses per year of dust, depending on the fraction of far-infrared sources that belong to the evolved star population (with 10%-50% uncertainty in individual dust-production rates). RSGs contribute the least (<4%), while carbon-rich AGB stars (especially the so-called "extreme" AGB stars) account for 87%-89% of the total dust input from cool evolved stars. We also estimate the dust input from hot stars and supernovae (SNe), and find that if SNe produce 10^-3 solar masses of dust each, then the total SN dust input and AGB input are roughly equivalent. We consider several scenarios of SNe dust production and destruction and find that the interstellar medium (ISM) dust can be accounted for solely by stellar sources if all SNe produce dust in the quantities seen around the dustiest examples and if most SNe explode in dense regions where much of the ISM dust is shielded from the shocks. We find that AGB stars contribute only 2.1% of the ISM dust. Without a net positive contribution from SNe to the dust budget, this suggests that dust must grow in the ISM or be formed by another unknown mechanism.