A dual AGN at z = 5.4 associated with a Lyman-alpha Nebula in the Center of a Cosmic Filament

Qiong Li, Christopher J. Conselice, Qiao Duan, Duncan Austin, Tom Harvey, Nathan Adams, George Bendo, Lewi Westcott, Vadim Rusakov, Zheng Cai, Yuanhang Ning, Shiwu Zhang

First listed 2025-08-13 | Last updated 2025-08-29

Abstract

Predictions from current theories and simulations suggest that dual AGN systems are exceedingly rare at high redshifts. The intense radiation and powerful outflows from AGNs regulate star formation, heat the interstellar medium, and drive massive gas outflows that shape the host galaxy and its surroundings. One manifestation of AGN feedback is the creation of extended Ly$α$ nebulae. However, identifying these systems at high-$z$ is challenging. Here, we report a remarkable dual AGN candidate at $z \sim 5.4$ using JWST NIRCam and NIRSpec, with a separation of $\sim1.7$ arcseconds ($\sim10.4$ pkpc). This is one of the highest spectroscopically confirmed redshift dual AGNs discovered. Photometric SED fitting shows excellent agreement with AGN templates, strongly suggesting a rare dual AGN system. BPT diagrams and high ionisation lines further support the presence of AGNs. VLT/MUSE observations reveal strong extended Ly$α$ emission, extending to $>22$ kpc, making it one of the most extended Ly$α$ nebulae at $z \sim 6$. This provides observational evidence of anisotropic AGN-driven photoionization or shocks. The high Ly$α$ escape fraction also indicates an AGN outflow. This dual AGN candidate is also associated with a well-defined overdensity, potentially at the center of a $z \sim 5.4$ protocluster or filamentary structure node. Further analysis indicates the fraction of dual AGNs is significantly higher than theoretically expected at high redshifts. This discovery provides a new opportunity to study dual AGN interactions and their impact on the circumgalactic medium and cosmic structure evolution.

Short digest

A systematic JWST search flags a spectroscopically confirmed close pair at z≈5.4 (G1: JADES 32751; G2: JADES 32927) with 1.7″ (10.4 pkpc) separation; both components show AGN signatures. NIRSpec PRISM (G1) and NIRCam/F444W grism from FRESCO (G2) reveal rest‑optical line ratios consistent with AGN on BPT diagnostics, with SED fits preferring AGN+SF templates and high‑ionization features strengthening the case. VLT/MUSE maps a >22 kpc Lyα nebula around G2 whose morphology and high Lyα escape fraction point to anisotropic AGN photoionization and an outflow. The pair sits in an overdense filament/protocluster node at z∼5.4, hinting that dual AGNs may be more common at early times than simulations predict and offering a clean probe of CGM feedback during early black‑hole growth.

Key figures to inspect

• Figure 1: Inspect the 1D+2D NIRSpec PRISM spectra for G1 and the grism spectrum for G2 to identify the rest‑optical lines driving the AGN classification (BPT placement, high‑ionization features), confirm the precise redshifts, and compare line widths/flux ratios between the two nuclei.
• Figure 2a–b: Use the NIRCam RGB for precise pair geometry and the MUSE Lyα pseudo–narrowband map with S/N contours to gauge the >22 kpc extent, anisotropy relative to the G1–G2 axis, and the fact that the emission likely extends beyond the MUSE footprint (so current size is a lower limit).
• Figure 2c: Examine the clumpy F090W morphology of G2 for sub‑arcsecond structures indicative of recent merger activity that could be fueling the AGN, and how these clumps align with the Lyα morphology.
• Figure 3: Compare AGN+SF (Nakajima) versus normal galaxy (FSPS+Larson) EAZY‑py fits for G1 and G2 to see the preference for AGN templates and where residuals concentrate (rest‑optical vs rest‑UV), reinforcing dual AGN SED evidence.
• Figure 4: Read the log‑normal vs continuity SFHs to verify both galaxies are in a starburst phase; note any differences in recent SFR peaks and mass build‑up that could correlate with AGN activity and the Lyα nebula strength.