The ionized gas outflow in the Circinus galaxy

Abstract

We employ MUSE/VLT data to study the ionized and highly ionized 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-ionization gas outflow beyond the galaxy plane traced by the coronal lines [Fe vii] λ6089 and [Fe x] λ6374, extending up to 700 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 active galactic nucleus (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-ionization gas is characterized by a temperature reaching 25 000 K and an electron density >102 cm−3. We found that local gas excitation by shocks produced by the passage of a radio jet leads to the spectacular high-ionization emission in this object. This hypothesis is fully supported by photoionization models that account 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 ionization 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.