Star-dust geometry main determinant of dust attenuation in galaxies

TL;DR

This study reveals that the geometry of stars and dust within galaxies, especially the distinction between spheroid and disc structures, is the main factor determining the variation in dust attenuation curves across different galaxy types.

Contribution

It demonstrates that star-dust geometry, rather than the extinction curve, primarily drives the differences in dust attenuation properties among galaxy structures.

Findings

Spheroid-dominated galaxies have nearly twice as steep attenuation curves as disc-dominated ones.

Structural type correlates with distinct ranges of attenuation slope values.

Attenuation becomes shallower with increasing stellar mass and optical depth within the same structural group.

Abstract

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.