$\text{Naˉpoˉwawaˉ‘enakaulua}$: a close quasar pair at cosmic dawn in the Aether survey

Abstract

We present the discovery and first characterization of $\text{Naˉpoˉwawaˉ‘enakaulua}$: the most compact known quasar pair candidate in the Epoch of Reionization, with a projected separation of only $0.98^{\prime \prime }$ ($\approx 5.56$ pkpc at $z\sim 6.08$) and a velocity offset of $\Delta v\simeq 15{\text{ km s}}^{-1}$. Using spectroscopy from JWST/NIRSpec IFU, as part of the $\text{Aether survey}$, Gemini/GNIRS and GMOS we characterize the continuum and emission line properties of the two quasars, enabling constraints on their black hole masses ($M_{\text{BH}}\simeq 1.5\times 10^9$ and $4.0\times 10^8{M}_{\odot }$), accretion states (${\lambda }_{\text{Edd}}\simeq 1.23$ and $1.07$), and systemic redshifts ($z_{\mathrm{sys}}\simeq 6.0781$ and $6.0785$). We place this pair in the cosmological context by comparing the chance of occurrence to extrapolations of high-$z$ quasar clustering measurements at larger scales, resulting in a $\sim 2-3$ order of magnitude excess with respect to expectations. This excess hints at an underlying population of merger-triggered quasar pairs at cosmic dawn or to a denser-than-average galactic environment. $\text{Naˉpoˉwawaˉ‘enakaulua}$ thus represents a crucial signpost to investigate the mass assembly of the first massive galaxies and black holes.

arXiv comment15 pages, 4 figures, 1 table. Under review for publication in ApJL