Systematic biases in determining dust attenuation curves through galaxy SED fitting

Abstract

While the slope of the dust attenuation curve ($\delta$) is found to correlate with effective dust attenuation ($A_V$) as obtained through spectral energy distribution (SED) fitting, it remains unknown how the fitting degeneracies shape this relation. We examine the degeneracy effects by fitting SEDs of a sample of local star-forming galaxies (SFGs) selected from the Galaxy And Mass Assembly survey, in conjunction with mock galaxy SEDs of known attenuation parameters. A well-designed declining starburst star formation history is adopted to generate model SED templates with intrinsic UV slope (${\beta }_0$) spanning over a reasonably wide range. The best-fitting ${\beta }_0$ for our sample SFGs shows a wide coverage, dramatically differing from the limited range of ${\beta }_0<-2.2$ for a starburst of constant star formation. Our results show that strong degeneracies between ${\beta }_0$, $\delta$, and $A_V$ in the SED fitting induce systematic biases leading to a false $A_V$--$\delta$ correlation. Our simulation tests reveal that this relationship can be well reproduced even when a flat $A_V$--$\delta$ relation is taken to build the input model galaxy SEDs. The variations in best-fitting $\delta$ are dominated by the fitting errors. We show that assuming a starburst with constant star formation in SED fitting will result in a steeper attenuation curve, smaller degeneracy errors, and a stronger $A_V$--$\delta$ relation. Our findings confirm that the $A_V$--$\delta$ relation obtained through SED fitting is likely driven by the systematic biases induced by the fitting degeneracies between ${\beta }_0$, $\delta$, and $A_V$.

21 pages, 13 figures, accepted for publication in the MNRAS, Comments welcome!

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• How Well Can We Measure Galaxy Dust Attenuation Curves? The Impact of the Assumed Star-Dust Geometry Model in SED Fitting
• Panchromatic Photometry of Low-redshift, Massive Galaxies Selected from SDSS Stripe 82
• Understanding the Universal Dust Attenuation Scaling Relation of Star-Forming Galaxies