A VLBI survey of compact broad absorption line quasars with balnicity index BI>0

TL;DR

This study uses high-resolution VLBI radio observations to analyze a sample of compact BAL quasars, revealing their structure, age, orientation, and relationships between radio and optical properties, providing insights into their nature and evolution.

Contribution

It presents the first high-resolution radio survey of BAL quasars with BI>0, linking their radio properties to absorption strength and orientation, and discussing their evolutionary stage.

Findings

High BI correlates with lower radio-loudness, suggesting larger viewing angles.

Most BAL quasars are compact, low-luminosity, with diverse jet powers.

Large BI values may be associated with lower jet power and short AGN lifetimes.

Abstract

We performed high resolution radio observations of a new sample of ten BAL quasars using both the VLBA and EVN at 5 GHz. All the selected sources have balnicity indices (BI) more than 0 and radio flux densities less than 80 mJy at 1.4 GHz. They are very compact with linear sizes of the order of a few tens of parsecs and radio luminosities at 1.4 GHz above the FRI-FRII luminosity threshold. Most of the observed objects have been resolved at 5 GHz showing one-sided, probably core-jet structures, typical for quasars. We discuss in detail their age and orientation based on the radio observations. We then used the largest available sample of BAL quasars to study the relationships between the radio and optical properties in these objects. We found that (1) the strongest absorption (high values of the balnicity index BI) is connected with the lower values of the radio-loudness parameter, logR_I<1.5, and thus probably with large viewing angles; (2) the large span of the BI values in each bin of the radio-loudness parameter indicates that the orientation is only one of the factors influencing the measured absorption; (3) most of the radio-loud BAL quasars are compact, low luminosity objects with a wide range of jet power (although the highest values of BI seem to be associated with the lower values of jet power). In addition, we suggest that the short lifetime postulated for some compact AGNs could also explain the scarcity of the large-scale radio sources among BAL quasars.