$\textit{N\=ap\=owaw\=a`enakaulua}$: a close quasar pair at cosmic dawn in the Aether survey

We report the discovery and first characterization of Nāpōwawā`enakaulua, the most compact known quasar pair candidate in the Epoch of Reionization. The pair has a projected separation of only 0.98 arcseconds (≈5.56 pkpc at z ~ 6.08) and a velocity offset of Δv ≈ 15 km s⁻¹.

Spectroscopy from JWST/NIRSpec IFU, as part of the Aether survey, along with Gemini/GNIRS and GMOS, was used to characterize the continuum and emission line properties of both quasars. This enabled constraints on their black hole masses, accretion states, and systemic redshifts.

The two black holes have masses M_BH ≈ 1.5 × 10^9 and 4.0 × 10^8 M_☉, with Eddington ratios λ_Edd ≈ 1.23 and 1.07, indicating near-Eddington accretion. Their systemic redshifts are z_sys ≈ 6.0781 and 6.0785.

Placing the pair in cosmological context, the authors compared its chance of occurrence to extrapolations of high-z quasar clustering measurements at larger scales. This yielded a ~2–3 order of magnitude excess relative to expectations. The excess hints at an underlying population of merger-triggered quasar pairs at cosmic dawn or a denser-than-average galactic environment. Nāpōwawā`enakaulua thus represents a crucial signpost for investigating the mass assembly of the first massive galaxies and black holes.