BEES: Quasar lifetime measurements from extended rest-optical emission line nebulae at $z\sim6$

Dominika Ďurovčíková, Anna-Christina Eilers, Yuzo Ishikawa, Minghao Yue, Marianne Vestergaard, Frederick B. Davies, Jan-Torge Schindler, Xiaohui Fan, Fabrizio Arrigoni Battaia, Marta Volonteri, Robert A. Simcoe, Joseph F. Hennawi, Laura Blecha, Irham T. Andika, Sarah E. I. Bosman, Rebekka Bieri

First listed 2025-10-10 | Last updated 2025-10-10

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 $z\sim6$ quasars have revealed that these short observed lifetimes are unlikely a sightline-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 IFU observations of five $z\sim 6$ 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 sightlines. 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, $t_{\rm Q} \lesssim 10^{5}\ {\rm yr}$, hosting billion-solar-mass black holes, indicating that rapid accretion is likely responsible for the assembly of SMBHs in the early Universe.

Short digest

JWST/NIRSpec IFU maps of five z∼6 quasars with small proximity zones reveal extended Hα and [O III]5007 nebulae in four cases, enabling transverse lifetime estimates from their light-crossing extents. The nebular sizes imply extremely short UV-luminous phases, t_Q ≲ 10^5 yr, and Hα confirms that recombination powers the previously reported Lyα halos. Rest-optical Hα/Hβ fits also yield ∼10^9 M⊙ black holes at these epochs, reinforcing a picture of rapid, episodic accretion to assemble early SMBHs.

Key figures to inspect

• Figure 1: Inspect the Hα and Hβ zoom-ins and MCMC component fits to see the broad-line widths and continuum/Fe II decomposition used for the ∼10^9 M⊙ BH mass estimates; check residuals for systematics near Balmer lines.
• Figure 2 (J0100+2802): Compare the PSF-subtracted pseudo–narrowband Hα and [O III] maps and SNR panels to verify genuine extended emission; use the annulus-averaged surface-brightness profiles to read off the maximum nebular radius that sets the transverse t_Q, noting the masked PSF core and IFU FoV limits.
• Figure 2 (right panels): Contrast Hα vs [O III] radial extents for J0100+2802 to gauge multiphase CGM structure and which line controls the lifetime constraint (larger detected radius → tighter t_Q).
• Figure 3 (J158–14): Repeat the PSF-subtracted map and profile reading to extract the nebular edge and corresponding t_Q; compare Hα to [O III] morphology to assess recombination dominance vs. harder-ionization zones.
• Figure 3 (right panels): Examine the noise-floor shading and hatched inaccessible regions to understand how the nebular cutoff—and thus the lifetime—was determined and limited by sensitivity and FoV.