How Well Can We Measure Galaxy Dust Attenuation Curves? The Impact of the Assumed Star-Dust Geometry Model in SED Fitting

Abstract

One of the most common methods for inferring galaxy attenuation curves is via spectral energy distribution (SED) modeling, where the dust attenuation properties are modeled simultaneously with other galaxy physical properties. In this paper, we assess the ability of SED modeling to infer these dust attenuation curves from broadband photometry, and suggest a new flexible model that greatly improves the accuracy of attenuation curve derivations. To do this, we fit mock SEDs generated from the simba cosmological simulation with the prospector SED fitting code. We consider the impact of the commonly-assumed uniform screen model and introduce a new non-uniform screen model parameterized by the fraction of unobscured stellar light. This non-uniform screen model allows for a non-zero fraction of stellar light to remain unattenuated, resulting in a more flexible attenuation curve shape by decoupling the shape of the UV attenuation curve from the optical attenuation curve. The ability to constrain the dust attenuation curve is significantly improved with the use of a non-uniform screen model, with the median offset in UV attenuation decreasing from −0.30 dex with a uniform screen model to −0.17 dex with the non-uniform screen model. With this increase in dust attenuation modeling accuracy, we also improve the star formation rates (SFRs) inferred with the non-uniform screen model, decreasing the SFR offset on average by 0.12 dex. We discuss the efficacy of this new model, focusing on caveats with modeling star-dust geometries and the constraining power of available SED observations.

Quenching and the UVJ Diagram in the SIMBA Cosmological Simulation

“…In summary, while the trends we observe in sSFR on the UVJ diagram are subtler than observed trends, this can be largely attributed to the fact that observations tend to assume a universal attenuation curve in spite of underlying variation. A full analysis of the dependence of galaxy properties derived from SEDs on the assumed attenuation curve is beyond the scope of this paper (though it is explored in more detail in Lower et al 2020Lower et al , 2022. That said, we note that a continual trend in sSFR on the UVJ diagram has been reproduced even with SED fitting codes that allow for a varying attenuation curve (e.g., Leja et al 2019).…”