A VLA Survey of Radio-Selected SDSS Broad Absorption Line Quasars

TL;DR

This study surveys radio-selected broad absorption line quasars using VLA observations, revealing their generally compact nature, spectral index differences from normal quasars, and implications for their orientation and structure.

Contribution

It provides the first detailed radio spectral analysis of a sizable BAL quasar sample, highlighting differences from non-BAL quasars and suggesting orientation effects.

Findings

BAL quasars are mostly compact at arcsecond resolution.

BAL quasars tend to have steeper radio spectral indices.

BAL quasars are likely observed at larger angles from the jet axis.

Abstract

We have built a sample of 74 radio-selected broad absorption line quasars from the Sloan Digital Sky Survey Data Release 5 (SDSS DR5) and Faint Images of the Radio Sky at Twenty Centimeters (FIRST), along with a well matched sample of 74 unabsorbed "normal" quasars. The sources have been observed with the NRAO Very Large Array/Expanded Very Large Array at 8.4 GHz (3.5 cm) and 4.9 GHz (6 cm). All sources have additional archival 1.4 GHz (21 cm) data. Here we present the measured radio fluxes, spectral indices, and our initial findings. The percentage of BAL quasars with extended structure (on the order of 10%) in our sample is similar to previous studies at similar resolutions, suggesting that BAL quasars are indeed generally compact, at least at arsecond resolutions. The majority of sources do not appear to be significantly variable at 1.4 GHz, but we find two previously unidentified BAL quasars that may fit into the "polar" BAL category. We also identify a significant favoring of steeper radio spectral index for BAL compared to non-BAL quasars. This difference is apparent for several different measures of the spectral index, and persists even when restricting the samples to only include compact objects. Because radio spectral index is a statistical indicator of viewing angle for large samples, these results suggest that BAL quasars do have a range of orientations but are more often observed farther from the jet axis compared to normal quasars.