Hot dust in Panchromatic SED Fitting: Identification of AGN and improved galaxy properties

TL;DR

This study enhances galaxy spectral energy distribution modeling by incorporating dusty AGN torii, revealing that neglecting AGN leads to significant biases in derived galaxy properties and that many AGN are missed by simple MIR color selection.

Contribution

The paper introduces the inclusion of dusty AGN torii in SED fitting, improving accuracy in galaxy property estimation and revealing many AGN are undetected by traditional MIR methods.

Findings

10% of galaxies host significant AGN contributions

Including AGN alters stellar ages and SFRs by up to a factor of 10

Only 46% of AGN are identified by MIR color selection

Abstract

Forward modeling of the full galaxy SED is a powerful technique, providing self-consistent constraints on stellar ages, dust properties, and metallicities. However, the accuracy of these results is contingent on the accuracy of the model. One significant source of uncertainty is the contribution of obscured AGN, as they are relatively common and can produce substantial mid-IR (MIR) emission. Here we include emission from dusty AGN torii in the Prospector SED-fitting framework, and fit the UV-IR broadband photometry of 129 nearby galaxies. We find that 10% of the fitted galaxies host an AGN contributing $>$10% of the observed galaxy MIR luminosity. We demonstrate the necessity of this AGN component in the following ways. First, we compare observed spectral features to spectral features predicted from our model fit to the photometry. We find that the AGN component greatly improves predictions for observed H$\alpha$ and H$\beta$ luminosities, as well as mid-infrared Akari and Spitzer/IRS spectra. Second, we show that inclusion of the AGN component changes stellar ages and SFRs by up to a factor of 10, and dust attenuations by up to a factor of 2.5. Finally, we show that the strength of our model AGN component correlates with independent AGN indicators, suggesting that these galaxies truly host AGN. Notably, only 46% of the SED-detected AGN would be detected with a simple MIR color selection. Based on these results, we conclude that SED models which fit MIR data without AGN components are vulnerable to substantial bias in their derived parameters.