Systematic biases in determining dust attenuation curves through galaxy SED fitting

TL;DR

This study investigates how degeneracies in galaxy SED fitting can create artificial correlations between dust attenuation curve slope and attenuation, highlighting the importance of accounting for systematic biases in such analyses.

Contribution

The paper demonstrates that the observed $A_V$--$ extdelta$ relation is primarily caused by fitting degeneracies, not intrinsic galaxy properties, emphasizing the need for careful modeling in SED fitting.

Findings

Degeneracies induce systematic biases in $A_V$--$ extdelta$ relation.

Simulations show the relation can be reproduced without intrinsic correlation.

Assuming constant star formation leads to steeper attenuation curves.

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 $A_V$.