The Contribution of Asymptotic Giant Branch Stars to the Infrared Luminosities of Galaxies

Using resolved stellar photometry in Hubble Space Telescope WFC3 images of 22 nearby galaxies, we measure the fraction of near-infrared (NIR) luminosity produced by short-lived asymptotic giant branch (AGB) stars. While AGB stars represent a negligible number fraction of stars in a given galaxy, they can contribute as much as 30% of the total NIR flux, even though local galaxies have large populations of red giant branch stars. In the early Universe, the AGB contribution to the total IR luminosity could be as high as 80%. For younger metal-rich galaxies, the AGB models used in this study tend to under-predict the contribution of the AGB to the galaxy's luminosity (at NIR wavelengths). The same models tend to over-predict the AGB for old metal-poor systems.