GA-NIFS: AGN activity in a Lyα emitter within a triple-AGN system anchored by a passive galaxy at z=3

Michele Perna, Santiago Arribas, Mahmoud Hamed, Francesco D'Eugenio, J. Andrew Bunker, Stefano Carniani, Stéphane Charlot, Roberto Maiolino, Bruno Rodríguez Del Pino, Hannah Übler, Torsten Böker, Elena Bertola, Giovanni Cresci, Isabella Lamperti, Giacomo Venturi, Michele Ginolfi, Montserrat Villar Martín, Sandra Zamora

First listed 2026-01-02 | Last updated 2026-01-02

Abstract

Massive quenched galaxies at z>3 challenge models of early galaxy evolution, as their rapid formation and abrupt quenching require efficient feedback, often linked to active galactic nuclei (AGN). The quiescent galaxy GS10578 at z=3.1 is a key example of this population. Previous JWST/NIRSpec IFU data revealed an AGN outflow and uncovered a compact pair of AGN separated by ~5 kpc. In addition, VLT/MUSE spectroscopy has identified a third AGN candidate at a projected distance of ~30 kpc, associated with a luminous Lya emitter (LAE2) characterised by high-ionisation UV lines, although rest-frame optical diagnostics were not previously available. We aim to confirm the nature of LAE2 using rest-frame optical diagnostics enabled by new JWST data, and to characterise the physical and ionisation properties of both LAE2 and a distinct nearby Lya emitter (LAE1) that lacks any detectable continuum counterpart. We analyse new NIRSpec IFU observations targeting the optical nebular lines of LAE1 and LAE2, complemented with MUSE data, as part of the GA-NIFS project. We extract integrated and spatially resolved spectra, construct emission-line maps, and use standard diagnostic diagrams to determine ionisation sources and kinematics. LAE2 exhibits line ratios fully consistent with an embedded AGN. Its optical lines display a clumpy morphology and irregular kinematics on sub-kpc scales. Except for Lya, LAE1 remains undetected in all nebular lines and in JWST imaging. The similarity of the LAE1 and LAE2 Lya profiles in both velocity and flux suggests that LAE1 traces resonantly scattered emission rather than in-situ star formation. Our analysis reveals that the environment of GS10578 contains both multi-black-hole activity and gas structures on tens-of-kpc scales, offering new insights into how feedback and satellite interactions influence the late evolutionary stages of quenched massive galaxies.

Short digest

New GA-NIFS NIRSpec IFU data (G235H/F170LP, 1.7–3.1 μm) target the rest-optical lines of two Lyα emitters around the quenched galaxy GS10578 (z=3.1) in a putative triple-AGN system. LAE2 is confirmed as an AGN: its BPT/He II diagnostics place it in the AGN regime, while [O III] and H maps show clumpy structure and irregular, non-rotating sub-kpc kinematics. LAE1 is Lyα-only and undetected in all optical nebular lines and JWST imaging; the close match between the LAE1 and LAE2 Lyα profiles in velocity and flux favors resonant scattering/fluorescence powered by LAE2, though in-situ star formation cannot be fully excluded. Together these data reveal multi–black-hole activity and tens-of-kpc gas structures surrounding a quenched massive galaxy, informing feedback and satellite-driven assembly at early times.

Key figures to inspect

• Fig. 1 — Use the NIRCam+MUSE context to locate GS10578, AGN-A/B, LAE1, and LAE2; verify the ∼30 kpc separations and the extended Lyα nebula that embeds the system and the NIRSpec IFU footprints.
• Fig. 2 — Inspect the integrated spectrum of LAE2 to see strong Hβ+[O III] and Hα, and the non-detections (He II 4687, [N II], [S II]) that set key upper limits for diagnostics.
• Fig. 3 — Examine [O III] and H flux maps and the velocity/moment-2 fields: note the clumpy emission, SE–NW velocity gradient, and the redshifted northern component inconsistent with simple disk rotation.
• Fig. 4 — Check where LAE2 falls on [N II]/Hα vs [O III]/Hβ and on [N II]/Hα vs He II/Hβ; the upper limit on optical He II and limits on [N II] still place it in the AGN regime, with a lower-limit variant using He II1640/4687 = 6.47.