Spectropolarimetry of Radio-Selected Broad Absorption Line Quasars

TL;DR

This study presents spectropolarimetric observations of 30 radio-selected BAL quasars, revealing polarization characteristics similar to radio-quiet BAL quasars and suggesting that orientation alone does not explain their properties.

Contribution

First spectropolarimetric analysis of radio-selected BAL quasars showing their polarization traits are akin to radio-quiet counterparts, challenging simple orientation models.

Findings

20% show large continuum polarization (2-10%)

Polarization rises toward shorter wavelengths

No correlation between polarization and radio properties

Abstract

We report spectropolarimetry of 30 radio-selected broad absorption line (BAL) quasars with the Keck Observatory, 25 from the sample of Becker et al. (2000). Both high and low-ionization BAL quasars are represented, with redshifts ranging from 0.5 to 2.5. The spectropolarimetric properties of radio-selected BAL quasars are very similar to those of radio-quiet BAL quasars: a sizeable fraction (20%) show large continuum polarization (2-10%) usually rising toward short wavelengths, emission lines are typically less polarized than the continuum, and absorption line troughs often show large polarization jumps. There are no significant correlations between polarization properties and radio properties, including those indicative of system orientation, suggesting that BAL quasars are not simply normal quasars seen from an edge-on perspective.