Determining the extragalactic extinction law with SALT. II. Additional sample

TL;DR

This study measures the extragalactic dust extinction law in seven E/S0 galaxies using SALT, finding it parallels the Galactic law and estimating dust masses, revealing a scale-free dust distribution.

Contribution

It provides new measurements of the extragalactic extinction law across multiple spectral bands in seven galaxies, and compares dust mass estimates with IRAS data.

Findings

Extinction law runs parallel to the Galactic curve with R_V=2.71±0.43.

Dust masses range from 10^4 to 10^7 Solar masses.

Dust distribution appears scale-free within ~60 pc regions.

Abstract

We present new results from an on-going programme to study the dust extragalactic extinction law in E/S0 galaxies with dust lanes with the Southern African Large Telescope (SALT) during its performance-verification phase. The wavelength dependence of the dust extinction for seven galaxies is derived in six spectral bands ranging from the near-ultraviolet atmospheric cutoff to the near-infrared. The derivation of an extinction law is performed by fitting model galaxies to the unextinguished parts of the image in each spectral band, and subtracting from these the actual images. We compare our results with the derived extinction law in the Galaxy and find them to run parallel to the Galactic extinction curve with a mean total-to-selective extinction value of 2.71+-0.43. We use total optical extinction values to estimate the dust mass for each galaxy, compare these with dust masses derived from IRAS measurements, and find them to range from 10^4 to 10^7 Solar masses. We study the case of the well-known dust-lane galaxy NGC2685 for which HST/WFPC2 data is available to test the dust distribution on different scales. Our results imply a scale-free dust distribution across the dust lanes, at least within ~1 arcsec (~60 pc) regions.