The Contribution of Thermally-Pulsing Asymptotic Giant Branch and Red Super Giant Stars to the Luminosities of the Magellanic Clouds at 1-24 um

TL;DR

This study quantifies the infrared flux contribution of TP-AGB and RSG stars to the Magellanic Clouds' luminosities, revealing their significant impact at specific wavelengths and implications for galaxy mass and star formation rate estimates.

Contribution

It provides the first detailed quantification of TP-AGB and RSG stars' flux contributions across 1-24 um in the Magellanic Clouds, informing stellar population modeling.

Findings

TP-AGB stars contribute up to 21% of galaxy flux at 3-4 um.

RSG stars contribute up to 11% at 2.2 um.

Evolved stars can bias star formation rate estimates from 8 um flux.

Abstract

We present the near- through mid-infrared flux contribution of thermally-pulsing asymptotic giant branch (TP-AGB) and massive red super giant (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 um, where they produce 32% of the SMC light, and 25% of the LMC flux. The TP-AGB star contribution also peaks at ~3-4 um and amounts to 21% in both galaxies. The contribution from RSG stars peaks at shorter wavelengths, 2.2 um, 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 ratios of galaxies at rest-frame 1-4 um. To minimize their impact on stellar mass estimates, one can use the M/L ratio at shorter wavelengths (e.g. at 0.8 - 1 um). At longer wavelengths (>=8 um), emission from dust in the interstellar medium dominates the flux. In the LMC, which shows strong PAH emission at 8 um, TP-AGB and RSG contribute less than 4% of the 8 um flux. However, 19% of the SMC 8 um 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 um flux (e.g. observed-frame 24 um at z=2), may be biased modestly high, especially for galaxies with little PAH emission.