Massive Extremely High-velocity Outflow in the Quasar J164653.72+243942.2

We present analysis of one of the most extreme quasar outflows found to date in our survey of extremely high-velocity outflows (EHVOs). J164653.72+243942.2 ( z em ∼ 3.04) shows variable C iv λλ 1548,1551 absorption at speeds larger than 0.1 c , accompanied by Si iv , N v, and Ly α , and disappearing absorption at lower speeds. We perform absorption measurements using the apparent optical depth method and SimBAL. We find the absorption to be very broad (Δ v ∼ 35,100 km s −1 in the first epoch and 13,000 km s −1 in the second one) and fast ( v max ∼ –50,200 km s −1 and −49,000 km s −1 , respectively). We measure large column densities ( log N H > 21.6 (cm −2 )) and are able to place distance estimates for the EHVO (5 ≲ R ≲ 28 pc) and the lower-velocity outflow (7 ≲ R ≲ 540 pc). We estimate a mass outflow rate for the EHVO to be M ̇ out ∼ 50 – 290 M ⊙ yr − 1 and a kinetic luminosity of log L KE ∼ 46.5 – 47.2 ( erg s − 1 ) in both epochs. The lower-velocity component has a mass outflow rate M ̇ out ∼ 10 – 790 M ⊙ yr − 1 and a kinetic luminosity of log L KE ∼ 45.3 – 47.2 ( erg s − 1 ) . We find that J164653.72+243942.2 is not an outlier among EHVO quasars in regard to its physical properties. While its column density is lower than typical BAL values, its higher outflow velocities drive most of the mass outflow rate and kinetic luminosity. These results emphasize the crucial role of EHVOs in powering quasar feedback, and failing to account for these outflows likely leads to underestimating the feedback impact on galaxies.