BAL Outflows are common in Low Eddington Ratio AGN

TL;DR

This study reveals that BAL quasar outflows are common in low Eddington ratio AGN, showing similar properties to high Eddington ratio sources and highlighting multiple driving mechanisms behind outflows.

Contribution

It is the first to compare BAL outflows across low and high Eddington ratios, revealing increased BAL fraction at low ratios and exploring underlying driving mechanisms.

Findings

BAL fraction increases toward low Eddington ratios

High Eddington sources exhibit more extreme absorption features

Outflow velocity correlates with Eddington ratio and luminosity

Abstract

Broad absorption line (BAL) quasars exhibit significant outflows, offering insights into active galactic nuclei (AGN) feedback. While typically associated with high Eddington ratios, BAL quasars also occur in low Eddington ratio regimes, which remain poorly understood. This study aims to compare BAL properties and variability across these regimes.We investigate the occurrence rates, absorption characteristics, and variability of BAL quasars at low and high Eddington ratios. Using the SDSS DR16 quasar catalog, we selected a redshift-matched control sample to compare low and high Eddington ratio BAL quasar sources. We first examined the BAL fraction as a function of Eddington ratio. Key absorption parameters-equivalent width, absorption line width, velocity range, and depth-were analyzed, and a multi-epoch variability study was conducted using repeat spectra, followed by a comparison of parameter distributions between the two samples. For the first time, we report an increase in BAL fraction toward low Eddington ratios, in addition to the previously known trend of high BAL fraction at high Eddington ratios. While high Eddington sources show extreme absorption features, overall distributions are statistically similar except for maximum outflow velocity. No significant variability differences were observed. The correlation between outflow velocity, Eddington ratio, and luminosity supports the role of radiation pressure in driving quasar outflows. For low Eddington ratios, additional mechanisms, such as softer SEDs, larger outflow distances, and thickened accretion disks from radiatively inefficient processes, likely drive outflow formation.