Kavli Affiliate: Yingjie Peng
| First 5 Authors: Jianbo Qin, Xian Zhong Zheng, Min Fang, Zhizheng Pan, Stijn Wuyts
| Summary:
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 $A_V$.
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