Kavli Affiliate: Robert A. Simcoe
| First 5 Authors: Dominika Ďurovčíková, Dominika Ďurovčíková, , ,
| Summary:
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$alpha$
nebulae around $zsim6$ quasars have revealed that these short observed
lifetimes are unlikely a sightline-dependent effect. However, the
interpretation of Ly$alpha$ 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 IFU observations of five $zsim 6$
quasars with small proximity zones to search for their extended emission line
nebulae in H$alpha$ 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 sightlines. Using their H$alpha$ nebulae, we also confirm that
recombination is likely the dominant emission mechanism behind their previously
detected Ly$alpha$ nebulae. Our results confirm the existence of high-redshift
quasars with extremely short lifetimes, $t_rm Q lesssim 10^5 rm yr$,
hosting billion-solar-mass black holes, indicating that rapid accretion is
likely responsible for the assembly of SMBHs in the early Universe.
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