A candidate quadruple AGN system at $z \sim 3$

TL;DR

This paper reports the discovery of a candidate quadruple AGN system at redshift around 3, potentially the second such system known, providing insights into protocluster environments and galaxy evolution.

Contribution

It presents a new candidate quadruple AGN system at high redshift, including detailed analysis of its components and implications for galaxy cluster formation.

Findings

Includes two SDSS quasars separated by ~480 kpc.

Identifies two additional AGN candidates at ~20 kpc separation.

Suggests the system may evolve into a galaxy cluster by z=0.

Abstract

Multiple galaxies hosting active galactic nuclei (AGNs) at kiloparsec separation from each other are exceedingly rare, and in fact, only one quadruple AGN is known so far. These extreme density peaks are expected to pinpoint protocluster environments and therefore be surrounded by large galaxy overdensities. In this letter, we present another quadruple AGN candidate at $z \sim 3$ including two SDSS quasars at a separation of roughly 480 kpc. The brighter quasar is accompanied by two AGN candidates (a type 1 AGN and a likely type 2 quasar) at close ($\sim 20$ kpc) separation identified through emission line ratios, line widths and high ionization lines like NV$\lambda1240$. The extended Ly$\alpha$ emission associated with the close triple system is more modest in extent and brightness compared to similar multiple AGN systems and could be caused by ram-pressure stripping of the type-2 quasar host during infall into the central dark matter halo. The predicted evolution of the system into a $z=0$ galaxy cluster with the AGN host galaxies forming the brightest cluster galaxy needs to be further tested by galaxy overdensity studies on large scales around the quadruple AGN candidate. If confirmed as a quadruple AGN with X-ray observations or rest-frame optical line ratios, this system would represent the second AGN quartet, the highest-redshift multiplet and the closest high-redshift triplet known.