The Mid-IR Contribution Of Dust Enshrouded Stars In Six Nearby Galaxies

TL;DR

This study quantifies the mid-infrared contribution of dusty AGB stars and luminous red sources in six nearby galaxies, revealing their small but significant role in galaxy mid-IR emission and its correlation with galaxy properties.

Contribution

It provides the first detailed measurement of dusty AGB stars' mid-IR contribution across multiple galaxies and explores its dependence on galaxy characteristics.

Findings

Dusty AGB stars contribute up to 5.6% at 3.6 microns and 10.1% at 4.5 microns.

The contribution of dusty AGB stars decreases with increasing galaxy metallicity and mass.

Red luminous sources contribute about 1.2% at 3.6 microns, with their dust likely cooler and more prominent at longer wavelengths.

Abstract

We measure the integrated contributions of dusty AGB stars and other luminous red mid-IR sources to the mid-IR luminosities of 6 galaxies (M81, NGC 2403, NGC 300, M33 and the Magellanic Clouds). We find the dusty AGB stars whose mid-IR fluxes are dominated by dust rather than photospheric emission contribute from 0.6% (M81) to 5.6% (SMC) of the 3.6 micron flux and 1.0% (M81) to 10.1% (SMC) of the 4.5 micron flux. We find a trend of decreasing AGB contribution with increasing galaxy metallicity, luminosity and mass and decreasing SSFR. However, these galaxy properties are strongly correlated in our sample and the simplest explanation of the trend is galaxy metallicity. Bright, red sources other than dusty AGB stars represent a smaller fraction of the luminosity, ~1.2% at 3.6 microns, however their dust is likely cooler and their contributions are likely larger at longer wavelengths. Excluding the SMC, the contribution from these red sources correlates with the specific star formation rate as we would expect for massive stars. In total, after correcting for dust emission at other wavelengths, the dust around AGB stars radiates 0.1-0.8% of the bolometric luminosities of the galaxies. Thus, hot dust emission from AGB and other luminous dusty stars represent a small fraction of the total luminosities of the galaxies but a significant fraction of their mid-IR emissions.