Probing Extreme Quasar Outflows through Broad Absorption Variability at High Redshift

Quasar-driven outflows are key to understanding supermassive black hole growth and AGN feedback, especially at high redshifts. Broad absorption lines (BALs) in quasar spectra provide a direct way to probe these outflows, particularly high-velocity systems that can strongly affect the host galaxy. We present results from a South African Large Telescope (SALT) monitoring campaign of C IV BAL variability in 64 high-redshift quasars (2 < z < 4) with outflow velocities above 15,000 km/s. This is one of the largest BAL monitoring programs to date, with near-annual cadence in the observer's frame (corresponding to a few months in the rest frame) over an eight-year period (2018–present). We carried out detailed analysis on interesting variability at both long and short timescales that includes large kinematic shifts in absorption (~1000 km/s), oscillatory changes in absorption strength on short timescales, and evidence for shielding between different outflow components within the same source. Using this dataset, we explore correlations between BAL properties, their variability, and global quasar properties. We also use state-of-the-art, spectral synthesis code 'SimBAL' to investigate the physical nature of these extreme outflows that suggests a distance of several tens to hundreds of parsecs to the outflow from the central engine. Our results highlight the importance of high-velocity BAL outflows for AGN feedback and also reveal several challenges for standard accretion disk wind models.