Circumstellar Dust Around AGB Stars and Implications for Infrared Emission from Galaxies

TL;DR

This paper introduces new circumstellar dust models for AGB stars, integrated into stellar population synthesis, to better understand IR emission from galaxies, especially in low-dust and low-metallicity environments.

Contribution

The authors developed and incorporated circumstellar dust models into SPS, improving IR emission predictions and matching observations of Magellanic Clouds and early-type galaxies.

Findings

Circumstellar dust significantly affects IR emission in low-dust galaxies.

Models fit IR color-magnitude diagrams of Magellanic Clouds.

Circumstellar dust has minimal impact on IR SEDs of metal-rich star-forming galaxies.

Abstract

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.