Star-dust geometry main determinant of dust attenuation in galaxies
  Analysing a large representative sample of local galaxies (8707), we find
that the variation in the shape of their dust attenuation curves is driven
primarily by their structure, i.e., distribution of stars (and dust) within
them. The attenuation curve for spheroid dominated galaxies, as compared to the
disc dominated ones, is nearly twice as steep. Both structural types cover
distinct ranges of attenuation slope values. Similar findings are reflected in
the case of star-forming and passive galaxies. Spheroids and passive galaxies
witness minimal attenuation in the optical compared to UV wavelengths
underlining the lack of dusty birth-clouds that define complex star-dust
geometry. The distinction in the attenuation properties of spheroids and discs
is maintained in each stellar mass range emphasising that structure is the
primal cause of variation. However, within a structural group, the attenuation
curve becomes shallower with both the increase in total stellar mass and
optical depth of the galaxy. Overall, with the extinction curve fixed to be the
same for all galaxies, the star-dust geometry emerges to be the prime
determinant of the variation in their attenuation properties.
