Precise physical conditions for the warm gas outflows in the nearby active galaxy IC 5063

TL;DR

This study uses spatially-resolved spectroscopy to accurately measure electron densities in the warm gas outflows of IC 5063, revealing shock compression effects and refining kinetic power estimates crucial for galaxy evolution models.

Contribution

First application of transauroral [SII] and [OII] lines for spatially-resolved electron density measurements in an active galaxy outflow, improving diagnostics of outflow properties.

Findings

Post-shock gas is denser than pre-shock gas, indicating shock compression.

Kinetic powers of warm ionised outflows are below galaxy evolution model requirements.

Warm ionised phase is dominated by AGN-photoionisation, while molecular phase shows composite excitation.

Abstract

AGN-driven outflows are now routinely used in models of galaxy evolution as a feedback mechanism, however many of their properties remain highly uncertain. Perhaps the greatest source of uncertainty is the electron density of the outflowing gas, which directly affects derived kinetic powers and mass outflow rates. Here we present spatially-resolved, wide spectral-coverage Xshooter observations of the nearby active galaxy IC 5063 (z=0.001131), which shows clear signatures of outflows being driven by shocks induced by a radio jet interacting with the ISM. For the first time, we use the higher critical-density transauroral [SII] and [OII] lines to derive electron densities in spatially-resolved observations of an active galaxy, and present evidence that the lines are emitted in the same spatial regions as other key diagnostic lines. In addition, we find that the post-shock gas is denser than the pre-shock gas, possibly due to shock compression effects. We derive kinetic powers for the warm ionised outflow phase and find them to be below those required by galaxy evolution models; however, other studies of different gas phases in IC 5063 allow us to place our results in a wider context in which the cooler gas phases constitute most of the outflowing mass. We investigate the dominant ionisation and excitation mechanisms and find that the warm ionised outflow phase is dominated by AGN-photoionisation, while the warm molecular phase has composite AGN-shock excitation. Overall, our results highlight the importance of robust outflow diagnostics and reinforce the utility of the transauroral lines for future studies of outflows in active galaxies.