A New Member of the Fast and Furious Family: A Relativistic and Time-variable UV Outflow in a Luminous Quasar

We report the fastest quasar outflow first detected in the ultraviolet, via variable C iv and Si iv absorption at outflow velocities −77,000 km s −1 to at least −90,000 km s −1 , in the radio-quiet quasar SDSS J231854.31+243954.2 (J2318). J2318 is a weak-lined quasar in the rest-frame ultraviolet, but Gemini GNIRS spectroscopy reveals an H α redshift of z = 2.6781 ± 0.0004. A 20 yr photometric time series shows peak-to-peak variability of 0.5 mag in the g band. The C iv outflow strengthened monotonically over three epochs spanning ∼2.2 rest-frame years. The existence of such a high-velocity outflow implies that models of quasar outflows must be able to either accelerate gas to 0.3 c while still preserving C iv and Si iv ions, or enable the formation of C iv and Si iv ions in gas, which has been accelerated to 0.3 c . Virial estimates reveal a black-hole mass of 1.65 × 10 9 M ⊙ , which leads to an Eddington luminosity and Eddington ratio of 2.4 × 10 47 erg s −1 and 0.45, respectively. Using very conservative assumptions, the UV-absorbing outflow alone has an estimated mass loss of >0.82 M ⊙ yr −1 and a kinetic luminosity ratio L kin / L bol ≥ 0.75%. The lower limit is just above the threshold usually cited for significant feedback on the host galaxy. Comparison to PDS 456, the only other known quasar with a UV-absorbing outflow at 0.3 c , suggests that the true M ̇ and L kin / L bol could be up to 2 orders of magnitude larger.