Discovery of a dual AGN at z~3.3 with 20kpc separation

TL;DR

This paper reports the discovery of a dual active galactic nucleus at redshift ~3.3 with a separation of 20 kpc, providing evidence for hierarchical galaxy assembly and dual black hole systems in the early universe.

Contribution

First detection of a dual AGN at z>3 with a separation of 20 kpc, demonstrating MUSE's capability to find such elusive systems in high-redshift galaxies.

Findings

Identified a second AGN within the LyA nebula of a z=3.286 QSO.

Confirmed the second source is likely an obscured AGN based on emission-line diagnostics.

Established this as the tightest known dual AGN at z>3.

Abstract

A prediction of the current paradigm of the hierarchical assembly of galaxies is the presence of supermassive dual black holes at separations of a few kpc or less. In this context, we report the detection of a narrow-line emitter within the extended LyA nebula (~120kpc diameter) of the luminous radio-quiet quasi-stellar object (QSO) LBQS0302-0019 at z=3.286. We identify several high-ionization narrow emission lines (HeII, CIV, CIII]) associated with this point-like source, which we have named "Jil", which is only ~20kpc (2.9") away from the QSO in projection. Emission-line diagnostics confirm that the source is likely powered by photoionization of an obscured active galactic nucleus (AGN) three orders of magnitude fainter than the QSO. The system represents the tightest unobscured/obscured dual AGN currently known at z>3, highlighting the power of MUSE to detect these elusive systems.