The effects of dust extinction on galaxy image decompositions

D. A. Gadotti

Combining Monte Carlo radiative transfer simulations and accurate 2D bulge/disc 
decompo- sitions, we present a new study to investigate the effects of dust 
attenuation on the apparent structural properties of the disc and bulge of 
spiral galaxies. We find that dust affects the results from such decompositions 
in ways which cannot be identified when one studies dust effects on bulge and 
disc components separately. In particular, the effects of dust in galaxies 
hosting pseudo-bulges might be different from those in galaxies hosting 
classical bulges, even if their dust content is identical. Confirming previous 
results, we find that disc scalelengths are overestimated when dust effects are 
important. In addition, we also find that bulge effec- tive radii and Se ́rsic 
indices are underestimated. Furthermore, the apparent attenuation of the 
integrated disc light is underestimated, whereas the corresponding attenuation 
of bulge light is overestimated. Dust effects are more significant for the 
bulge parameters, and, combined, they lead to a strong underestimation of the 
bulge-to-disc ratio, which can reach a factor of 2 in the V band, even at 
relatively low galaxy inclinations and dust opacities. Nevertheless, it never 
reaches factors larger than about 3, which corresponds to a factor of 2 in 
bulge-to-total ratio. Such effect can have an impact on studies of the black 
hole/bulge scaling relations.