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Published February 10, 2013 | Published
Journal Article Open

The Contribution of Thermally-pulsing Asymptotic Giant Branch and Red Supergiant Stars to the Luminosities of the Magellanic Clouds at 1-24 μm

Abstract

We present the near-through mid-infrared flux contribution of thermally-pulsing asymptotic giant branch (TP-AGB) and massive red supergiant (RSG) stars to the luminosities of the Large and Small Magellanic Clouds (LMC and SMC, respectively). Combined, the peak contribution from these cool evolved stars occurs at ~3-4 μm, where they produce 32% of the SMC light, and 25% of the LMC flux. The TP-AGB star contribution also peaks at ~3-4 μm and amounts to 21% in both galaxies. The contribution from RSG stars peaks at shorter wavelengths, 2.2 μm, where they provide 11% of the SMC flux, and 7% for the LMC. Both TP-AGB and RSG stars are short lived, and thus potentially impose a large stochastic scatter on the near-IR derived mass-to-light (M/L) ratios of galaxies at rest-frame 1-4 μm. To minimize their impact on stellar mass estimates, one can use the M/L ratio at shorter wavelengths (e.g., at 0.8-1 μm). At longer wavelengths (≥8 μm), emission from dust in the interstellar medium dominates the flux. In the LMC, which shows strong polycyclic aromatic hydrocarbon (PAH) emission at 8 μm, TP-AGB and RSG contribute less than 4% of the 8 μm flux. However, 19% of the SMC 8 μm flux is from evolved stars, nearly half of which is produced by the rarest, dustiest, carbon-rich TP-AGB stars. Thus, star formation rates of galaxies, based on an 8 μm flux (e.g., observed-frame 24 μm at z = 2), may be biased modestly high, especially for galaxies with little PAH emission.

Additional Information

© 2013 American Astronomical Society. Received 2012 August 9; accepted 2012 December 12; published 2013 January 22. Special thanks to Karl Gordon for providing integrated fluxes of the LMC in the Spitzer bands, and to Caroline Bot for sharing the SED and model fits of the Magellanic Clouds. Thanks to Gustavo Bruzual for sharing updated single stellar population models of the Magellanic Clouds.We also thank Barry Madore, Mark Seibert, andWendy Freedman for inspiring efforts to study the impact of AGB stars on mid-infrared galaxy fluxes. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

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