Measuring the dust attenuation law of galaxies using photometric data

ABSTRACT Fitting model spectral energy distributions (SEDs) to galaxy photometric data is a widely used method to recover galaxy parameters from galaxy surveys. However, the parameter space used to describe galaxies is wide and interdependent, and distinctions between real and spurious correlations that are found between these parameters can be difficult to discern. In this work, we use the SED fitting code bagpipes (Bayesian Analysis of Galaxies for Physical Inference and Parameter EStimation) to investigate degeneracies between galaxy parameters and the effect of the choice of different sets of photometric bands. In particular, we focus on optical to infrared wavelength coverage, and on two parameters describing the galaxies’ dust attenuation law: AV and δ, which characterize dust column density and the slope of a flexible dust attenuation law, respectively. We demonstrate that (1) a degeneracy between the residual (the difference between truth and recovered values) AV and star formation rate exists, but this is lifted when Wide-Field Infrared Survey Explorer bands are included, and (2) bagpipes is able to accurately recover the input AV and δ distributions and relations (differences in slope of less than 1.7σ for a flat relation and less than 1.2σ for an observationally motivated relation) and is not introducing spurious correlations between these parameters. Our findings suggest that the information needed to constrain AV and δ well enough individually exists in the data, especially when infrared is added. This indicates that recent works finding a correlation between AV and δ are not being misled by fitting degeneracies from their SED fitting code.