Abstract
Abstract We compare the infrared excess (IRX) and Balmer decrement ( ) as dust attenuation indicators in relation to other galaxy parameters using a sample of ∼32,000 local star-forming galaxies (SFGs) carefully selected from the Sloan Digital Sky Survey, the Galaxy Evolution Explorer, and the Wide-field Infrared Survey Explore. While at fixed , IRX turns out to be independent on galaxy stellar mass, the Balmer decrement does show a strong mass dependence at fixed IRX. We find the discrepancy, parameterized by the color excess ratio , is not dependent on the gas-phase metallicity and axial ratio, but on the specific star formation rate (SSFR) and galaxy size (R e) following . This finding reveals that the nebular attenuation as probed by the Balmer decrement becomes increasingly larger than the global (stellar) attenuation of SFGs with decreasing SSFR surface density. This can be understood in the context of an enhanced fraction of intermediate-age stellar populations that are less attenuated by dust than the H ii region-traced young population, in conjunction with a decreasing dust opacity of the diffuse interstellar matter when spreading over a larger spatial extent. Once the SSFR surface density of an SFG is known, the conversion between attenuation of nebular and stellar emission can be well estimated using our scaling relation.
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