Circumstellar Dust Around AGB Stars and Implications for Infrared
  Emission from Galaxies
  Stellar population synthesis (SPS) models are used to infer many galactic
properties including star formation histories, metallicities, and stellar and
dust masses. However, most SPS models neglect the effect of circumstellar dust
shells around evolved stars and it is unclear to what extent they impact the
analysis of SEDs. To overcome this shortcoming we have created a new set of
circumstellar dust models, using the radiative transfer code DUSTY Ivezic et
al. 1999, for asymptotic giant branch (AGB) stars and incorporated them into
the Flexible Stellar Population Synthesis code. The circumstellar dust models
provide a good fit to individual AGB stars as well as the IR color-magnitude
diagrams of the Large and Small Magellanic Clouds. IR luminosity functions from
the Large and Small Magellanic Clouds are not well-fit by the 2008 Padova
isochrones when coupled to our circumstellar dust models, and so we adjusted
the lifetimes of AGB stars in the models to provide a match to the data. We
show, in agreement with previous work, that circumstellar dust from AGB stars
can make a significant contribution to the IR ($\gtrsim4\mu m$) emission from
galaxies that contain relatively little diffuse dust, including low-metallicity
and/or non-star forming galaxies. Our models provide a good fit to the mid-IR
spectra of early-type galaxies. Circumstellar dust around AGB stars appears to
have a small effect on the IR SEDs of metal-rich star-forming galaxies (i.e.,
when A$_{\rm V}$ $\gtrsim$~0.1). Stellar population models that include
circumstellar dust will be needed to accurately interpret data from the James
Webb Space Telescope (JWST) and other IR facilities.
