Ultraviolet Dust Grain Properties in Starburst Galaxies: Evidence from Radiative Transfer Modeling and Local Group Extinction Curves

This paper summarizes the evidence of the ultraviolet properties of dust grains found in starburst galaxies. Observations of starburst galaxies clearly show that the 2175 Å feature is weak or absent. This can be the result of radiative transfer effects (mixing the dust and stars) or due to dust grains which do not have this feature. Spherical DIRTY radiative transfer models imply that it is not radiative transfer effects, but other radiative transfer models with disk/bulge geometries have found cases where it could be radiative transfer effects. Recent work on the extinction curves in the Magellanic Clouds and Milky Way has revealed that the traditional explanation of low metallicity for the absence of the 2175 Å feature in the Small Magellanic Cloud is likely incorrect. The SMC has one sightline with a 2175 Å feature and the Milky Way has sightlines without this feature. In addition, where the 2175 Å feature is found to be weak or absent in both Magellanic Clouds and the Milky Way, there is evidence for recent star formation. Taking the sum of the radiative transfer modeling of starburst galaxies and the behavior of Local Group extinction curves, it is likely that the dust grains in starburst galaxies intrinsically lack the 2175 Å feature.