BEES: Quasar Lifetime Measurements from Extended Rest-optical Emission Line Nebulae at z ∼ 6

Abstract Measurements of quasar lifetimes at high redshift indicate that the earliest billion-solar-mass supermassive black holes (SMBHs) have only been active as luminous quasars for less than a million years. Recently, extended Ly α nebulae around z ∼ 6 quasars have revealed that these short observed lifetimes are unlikely to be a sight-line-dependent effect. However, the interpretation of Ly α emission is not straightforward due to its resonant nature. In this work, we use rest-frame optical emission lines, which more directly trace photoionization by the quasar, to unambiguously validate the short line-of-sight quasar lifetimes observed at early cosmic epochs. We use deep James Webb Space Telescope/NIRSpec integral field unit observations of five z ∼ 6 quasars with small proximity zones to search for their extended emission line nebulae in H α and [O III ]5007, and detect extended emission in both emission lines around four quasars in our sample. We then use the light-crossing time of these nebulae to measure quasar lifetimes along transverse sight lines. Using their H α nebulae, we also confirm that recombination is likely the dominant emission mechanism behind their previously detected Ly α nebulae. Our results confirm the existence of high-redshift quasars with extremely short lifetimes, t Q ≲ 10 5 yr, hosting billion-solar-mass black holes, indicating that rapid or obscured accretion is likely responsible for the assembly of SMBHs in the early Universe.