Connecting radio emission to AGN wind properties with Broad Absorption Line Quasars

TL;DR

This study investigates the radio properties of Broad Absorption Line Quasars (BALQSOs) using LOFAR data, revealing correlations between radio detection, wind strength, and reddening, and suggesting wind-ISM interactions as a key factor.

Contribution

It provides the largest radio-matched BALQSO sample to date and links radio detection fractions to wind and reddening properties, offering new insights into BALQSO outflows.

Findings

BALQSOs are more radio-detected than non-BALQSOs by 1.5 times.

LoBALs show a 2.22 times higher detection rate than non-BALQSOs.

Radio detection correlates with wind strength, reddening, and C IV emission properties.

Abstract

Broad Absorption Line Quasars (BALQSOs) show strong signatures of powerful outflows, with the potential to alter the cosmic history of their host galaxies. These signatures are only seen in ~10% of optically selected quasars, although the fraction significantly increases in IR and radio selected samples. A proven physical explanation for this observed fraction has yet to be found, along with a determination of why this fraction increases at radio wavelengths. We present the largest sample of radio matched BALQSOs using the LOFAR Two-metre Sky Survey Data Release 2 and employ it to investigate radio properties of BALQSOs. Within the DR2 footprint, there are 3537 BALQSOs from Sloan Digital Sky Survey DR12 with continuum signal to noise >5. We find radio-detections for 1108 BALQSOs, with an important sub-population of 120 LoBALs, an unprecedented sample size for radio matched BALQSOs given the LoTSS sky coverage to date. BALQSOs are a radio-quiet population that show an increase of $\times 1.50$ radio-detection fraction compared to non-BALQSOs. LoBALs show an increase of $\times 2.22$ that of non-BALQSO quasars. We show that this detection fraction correlates with wind-strength, reddening and C_{IV} emission properties of BALQSOs and that these features may be connected, although no single property can fully explain the enhanced radio detection fraction. We create composite spectra for sub-classes of BALQSOs based on wind strength and colour, finding differences in the absorption profiles of radio-detected and radio-undetected sources, particularly for LoBALs. Overall, we favour a wind-ISM interaction explanation for the increased radio-detection fraction of BALQSOs.