VLT Spectropolarimetry of Broad Absorption Line QSOs

TL;DR

This study uses VLT spectropolarimetry to analyze the polarization properties of a diverse sample of BAL quasars, confirming known behaviors and identifying new correlations between polarization and luminosity or emission-line features.

Contribution

It provides new spectropolarimetric data for a broad range of BAL quasars, confirming previous findings and revealing correlations between polarization and quasar properties.

Findings

Continuum polarization generally rises at shorter wavelengths.

High broad-band polarization observed in 6 of 19 quasars.

Correlations found between polarization, luminosity, and emission-line polarization.

Abstract

We present spectropolarimetry of 19 confirmed and 4 possible bright, southern broad absorption line (BAL) quasars from the European Southern Observatory (ESO) Very Large Telescope (VLT). A wide range of redshifts is covered in the sample (from 0.9 to 3.4), and both low- and hi-ionization quasars are represented, as well as radio-loud and radio-quiet BALQSOs. We continue to confirm previously established spectropolarimetric properties of BALQSOs, including the generally rising continuum polarization with shorter wavelengths and comparatively large fraction with high broad-band polarization (6 of 19 with polarizations >2%). Emission lines are polarized less than or similar to the continuum, except in a few unusual cases, and absorption troughs tend to have higher polarizations. A search for correlations between polarization properties has been done, identifying 2 significant or marginally significant correlations. These are an increase in continuum polarization with decreasing optical luminosity (increasing absolute B magnitude) and decreasing \ion{C}{4} emission-line polarization with increased continuum polarization.