Extinction properties of lensing galaxies

TL;DR

This study investigates the dust extinction properties of lensing galaxies by analyzing the colors of gravitationally-lensed quasars, revealing a broad range of dust characteristics similar to those in the Milky Way.

Contribution

It provides the first comprehensive analysis of dust extinction laws in lensing galaxies using a sample of 21 systems, expanding understanding of dust properties at various redshifts.

Findings

Significant dust extinction detected in intervening galaxies.

Good fits to standard extinction laws for over half of the images.

Distribution of Rv values suggests dust properties similar to the Milky Way.

Abstract

Context. Observations of quasars shining through foreground galaxies, offer a way to probe the dust extinction curves of distant galaxies. Interesting objects for this study are found in strong gravitational lensing systems, where the foreground galaxies generate multiple images. Aims. The reddening law of lensing galaxies is investigated by studying the colours of gravitationally-lensed quasars, and a handful of other quasars where a foreground galaxy is detected. Methods. We compare the observed colours of quasars reported in the literature, with spectral templates reddened by different extinction laws and dust properties. The data consists of 21 quasar-galaxy systems, with a total of 48 images. The galaxies, which are both early- and late-type, have redshifts in the interval z=0.04-1.51. Results. We measure a difference in rest-frame B-V between the quasar images we study, and quasars without resolved foreground galaxies. This difference in colour is indicative of significant dust extinction in the intervening galaxy. Good fits to standard extinction laws were found for 22 of the images, corresponding to 13 different galaxies. Our fits imply a wide range of possible values for the total-to-selective extinction ratio, Rv. The distribution was found to be broad with a weighted mode of Rv=2.4 and a FWHM of 2.7 (sigma = 1.1). Thus the bulk of the galaxies for which good reddening fits could be derived, have dust properties compatible with the Milky Way value (Rv=3.1).