A VLBI survey of compact Broad Absorption Lines (BAL) quasars with BALnicity Index BI=0

TL;DR

This study uses high-resolution VLBI observations to image 14 compact BAL quasars, revealing their core-jet structures and suggesting they are young, luminous AGNs with absorption properties influenced by orientation and radio emission strength.

Contribution

First high-resolution VLBI imaging of AI-selected BAL quasars, revealing their morphology, luminosity, and the relationship between absorption and radio properties, highlighting the role of orientation and other factors.

Findings

Most sources show core-jet morphology typical for radio-loud quasars.

AI quasars are among the most luminous, small-sized AGNs.

Absorption strength correlates with lower radio-loudness, indicating orientation effects.

Abstract

We present high-resolution observations, using both the European VLBI Network (EVN) at 1.7-GHz, and the Very Long Baseline Array (VLBA) at 5 and 8.4-GHz to image radio structures of 14 compact sources classified as broad absorption line (BAL) quasars based on the absorption index (AI). All source but one were resolved, with the majority showing core-jet morphology typical for radio-loud quasars. We discuss in details the most interesting cases. The high radio luminosities and small linear sizes of the observed objects indicate they are strong young AGNs. Nevertheless, the distribution of the radio-loudness parameter, log(Ri), of a larger sample of AI quasars shows that the objects observed by us constitute the most luminous, small subgroup of AI population. Additionally we report that for the radio-loudness parameter, the distribution of AI quasars and those selected by using the traditional balnicity index (BI), BI quasars differ significantly. Strong absorption is connected with the lower log(Ri), and thus probably with larger viewing angles. Since, the AI quasars have on average larger log(Ri), the orientation can cause that we see them less absorbed. However, we suggest that the orientation is not the only parameter that affects the detected absorption. The fact that the strong absorption is associated with the weak radio emission is equally important and worth exploring.