Michael A. DiPompeo, Michael S. Brotherton, Carlos De Breuck, Sally Laurent-Muehleisen
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.
View original:
http://arxiv.org/abs/1110.4916
No comments:
Post a Comment