Determining the extragalactic extinction law with SALT

TL;DR

This study uses SALT imaging to analyze the extinction law of extragalactic dust in dark lanes, finding it similar to the Milky Way's dust properties and providing insights into dust grain sizes in other galaxies.

Contribution

First measurement of extragalactic extinction law using SALT, showing similarity to Galactic dust and estimating the V-band extinction ratio in dark lane galaxies.

Findings

Extinction curves are parallel to the Galactic curve.

The average R_V value is 2.82, close to Milky Way's 3.1.

Dust grain sizes are comparable to Galactic dust.

Abstract

We present CCD imaging observations of early-type galaxies with dark lanes obtained with the Southern African Large Telescope (SALT) during its performance-verification phase. We derive the extinction law by the extragalactic dust in the dark lanes in the spectral range 1.11mu m^{-1} < lambda^{-1} < 2.94 mu m^{-1} by fitting model galaxies to the unextinguished parts of the image, and subtracting from these the actual images. We find that the extinction curves run parallel to the Galactic extinction curve, which implies that the properties of dust in the extragalactic enviroment are similar to those of the Milky Way. The ratio of the total V band extinction to the selective extinction between the V and B bands is derived for each galaxy with an average of 2.82+-0.38, compared to a canonical value of 3.1 for the Milky Way. The similar values imply that galaxies with well-defined dark lanes have characteristic dust grain sizes similar to those of Galactic dust.