The MURALES survey. I. A dual AGN in the radio galaxy 3C459?

TL;DR

This study uses VLT/MUSE observations to identify a dual AGN system in the radio galaxy 3C459, revealing complex ionized gas structures and providing evidence for a recent merger involving a radio loud AGN and a type 2 QSO.

Contribution

First detailed spectroscopic evidence for a dual AGN in 3C459, combining ionized gas morphology, kinematics, and line ratios to distinguish between AGN and jet-cloud interaction.

Findings

Detection of two compact emission regions with distinct velocities and line ratios.

Evidence supporting a dual AGN system rather than jet-cloud interaction.

Identification of a high-ionization bicone associated with N2.

Abstract

We observed the FRII radio galaxy 3C459 (z=0.22) with the MUSE spectrograph at the Very Large Telescope (VLT) as part of the MURALES project (a MUse RAdio Loud Emission line Snapshot survey). We detected diffuse nuclear emission and a filamentary ionized gas structure forming a one-sided, triangular-shaped region extending out to $\sim$80 kpc. The central emission line region is dominated by two compact knots of similar flux: the first (N1) cospatial with the radio core and the (N2) second located 1.2" (5.3 kpc) to the SE. The two regions differ dramatically from the point of view of velocity (with an offset of ~400 km/s), line widths, and line ratios. This suggests that we are observing a dual AGN system formed by a radio loud AGN and type 2 QSO companion, which is the result of the recent merger that also produced its disturbed host morphology. The alternative possibility that N2 is just a bright emission line knot resulting from, for example, a jet-cloud interaction, is disfavored because of 1) the presence of a high ionization bicone whose apex is located at N2; 2) the observed narrow line widths; 3) its line luminosity (~10^42 erg s-1) typical of luminous QSOs; and 4) its location, which is offset from the jet path. The putative secondary AGN must be highly obscured, since we do not detect any emission in the Chandra and infrared Hubble Space Telescope images.