PS J1721+8842: A gravitationally lensed dual AGN system at redshift 2.37 with two radio components

TL;DR

This paper reports the discovery of a gravitationally lensed dual-AGN system at redshift 2.37, featuring two quasars with associated radio emission, providing insights into black hole growth and galaxy formation during peak cosmic epochs.

Contribution

First identification of a high-redshift gravitationally lensed dual-AGN system with detailed radio and optical/IR observations, advancing understanding of galaxy mergers and black hole evolution.

Findings

Detected two quasars separated by ~6.5 kpc with associated radio emission.

Radio luminosities suggest weak jets or star formation activity.

System may be a triple-merger or post-merger black hole recoil scenario.

Abstract

Dual-Active Galactic Nuclei (AGN) are a natural consequence of the hierarchical structure formation scenario, and can provide an important test of various models for black hole growth. However, due to their rarity and difficulty to find at high redshift, very few confirmed dual-AGN are known at the epoch where galaxy formation peaks. Here we report the discovery of a gravitationally lensed dual-AGN system at redshift 2.37 comprising two optical/IR quasars separated by 6.5+/-0.6 kpc, and a third compact (R_eff = 0.45+/-0.02 kpc) red galaxy that is offset from one of the quasars by 1.7+/-0.1 kpc. From Very Large Array imaging at 3 GHz, we detect 600 and 340 pc-scale radio emission that is associated with both quasars. The 1.4 GHz luminosity densities of the radio sources are about 10^24.35 W / Hz, which is consistent with weak jets. However, the low brightness temperature of the emission is also consistent with star-formation at the level of 850 to 1150 M_sun / yr. Although this supports the scenario where the AGN and/or star-formation is being triggered through an ongoing triple-merger, a post-merger scenario where two black holes are recoiling is also possible, given that neither has a detected host galaxy.