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