The Quasar - frame Velocity Distribution of Narrow C IV

We report on a survey for narrow (FWHM < 600 km s) C iv absorption lines in a sample of bright quasars at redshifts 1.8 6 z < 2.25 in the Sloan Digital Sky Survey. Our main goal is to understand the relationship of narrow C iv absorbers to quasar outflows and, more generally, to quasar environments. We determine velocity zeropoints using the broad Mg ii emission line, and then measure the absorbers’ quasarframe velocity distribution. We examine the distribution of lines arising in quasar outflows by subtracting model fits to the contributions from cosmologically intervening absorbers and absorption due to the quasar host galaxy or cluster environment. We find a substantial number (> 43±6 per cent) of absorbers with W 0 > 0.3 Å in the velocity range +750 km s . v . +12000 kms are intrinsic to the AGN outflow. This ‘outflow fraction’ peaks near v = +2000 km s with a value of foutflow ≃ 0.81±0.13. At velocities below v ≈ +2000 kms the incidence of outflowing systems drops, possibly due to geometric effects or to the over-ionization of gas that is nearer the accretion disk. Furthermore, we find that outflow-absorbers are on average broader and stronger than cosmologically-intervening systems. Finally, we find that ∼ 14 per cent of the quasars in our sample exhibit narrow, outflowing C iv absorption with W 0 > 0.3Å, slightly larger than that for broad absorption line systems.