The Extreme High-Velocity Outflow in Quasar PG0935+417

TL;DR

This paper reports the discovery of an extremely high-velocity quasar outflow in PG0935+417, characterized by variable absorption lines indicating a highly ionized, fast-moving gas with unique properties challenging existing models of quasar winds.

Contribution

It provides detailed observational evidence of an ultra-fast outflow with velocities around -50,000 km/s and discusses its implications for models of quasar outflows and ionization conditions.

Findings

Detected high-velocity OVI and NV absorption lines.

Estimated a total hydrogen column density of ~5 x 10^19 cm^-2.

Observed variability in absorption features over 15 years.

Abstract

We report the detection of OVI 1031,1037 and NV 1238,1242 absorption in a system of "mini-broad" absorption lines (mini-BALs) previously reported to have variable CIV 1548,1550 in the quasar PG0935+417. The formation of these lines in an extreme high-velocity quasar outflow (with v ~ -50000 km/s) is confirmed by the line variability, broad smooth absorption profiles, and partial covering of the background light source. HI and lower ionization metals are not clearly present. The resolved OVI doublet indicates that these lines are moderately saturated, with the absorber covering ~80% of the quasar continuum source (C_f~0.8). We derive ionic column densities of order 1015 cm^(-2) in CIV and several times larger in OVI, indicating an ionization parameter of log U >~ -0.5. Assuming solar abundances, we estimate a total column density of N(H) ~5 x 10^(19) cm^(-2). This outflow emerged sometime between 1982 and 1993. Our examination of the CIV data from 1993 to 2007 shows that there is variable complex absorption across a range of velocities from -45000 to -54000 km/s. There is no clear evidence for acceleration or deceleration of the outflow gas. Outflows are common in Active Galactic Nuclei (AGN), but extreme speeds such as those reported here are extremely rare. It is not clear what properties of PG0935+417 might produce this unusual outflow. In fact, PG0935+417 has significantly less X-ray absorption than typical BAL quasars even though its outflow has a degree of ionization typical of BALs at speeds that are 2-3 times larger than most BALs. These results might present a challenge to theoretical models that invoke strong radiative shielding in the X-rays/far-UV to moderate the outflow ionization and thus enable its radiative acceleration to high speeds.