Extreme-velocity quasar outflows and the role of X-ray shielding

Abstract

Quasar accretion disc winds observed via broad absorption lines (BALs) in the UV produce strong continuous absorption in X-rays. The X-ray absorber is believed to serve critically as a radiative shield to keep the outflow ionizations low enough for radiative driving. However, previous studies have shown that 'mini-BAL' and narrow absorption line (NAL) outflows have dramatically less X-ray absorption than BALs. Here, we examine X-ray and rest-frame UV spectra of eight mini-BAL quasars with outflow speeds in the range 0.1-0.2c to test the hypothesis that these extreme speeds require a strong shield.We find that theX-ray absorption is weak or moderate, with neutral-equivalent column densities NH