The ionised gas outflow in the Circinus galaxy: kinematics and physical conditions

TL;DR

This study uses MUSE/VLT data to analyze ionised gas outflows in the Circinus galaxy, revealing high-ionisation gas extending far from the nucleus, driven by shocks from a radio jet, and linking to molecular outflows.

Contribution

First detection of [Fe X] emission at large distances in an AGN, demonstrating the impact of radio jets on ionised gas and feedback processes in Circinus.

Findings

High-ionisation gas extends up to 700 pc from the nucleus.

Radio jet-driven shocks produce high-ionisation emission.

Correlation between ionised and molecular outflows suggests linked feedback mechanisms.

Abstract

We employ MUSE/VLT data to study the ionised and highly ionised gas phases of the feedback in Circinus, the closest Seyfert 2 galaxy to us. The analysis of the nebular emission allowed us to detect a remarkable high-ionisation gas outflow beyond the galaxy plane traced by the coronal lines [Fe VII] $\lambda$6089 and [Fe X] $\lambda$6374, extending up to 700 pc and 350 pc NW from the nucleus, respectively. This is the first time that the [Fe X] emission is observed at such distances from the central engine in an AGN. The gas kinematics reveals expanding gas shells with velocities of a few hundred km s$^{-1}$, spatially coincident with prominent hard X-ray emission detected by Chandra. Density and temperature sensitive line ratios show that the extended high-ionisation gas is characterized by a temperature reaching 25000 K and an electron density > 10$^2$ cm$^{-3}$. We found that local gas excitation by shocks produced by the passage of a radio jet leads to the spectacular high-ionisation emission in this object. This hypothesis is fully supported by photoionisation models that accounts for the combined effects of the central engine and shocks. They reproduce the observed emission line spectrum at different locations inside and outside of the NW ionisation cone. The energetic outflow produced by the radio jet is spatially located close to an extended molecular outflow recently reported using ALMA which suggests that they both represent different phases of the same feedback process acting on the AGN.