Dissecting the active galactic nucleus in Circinus IV. MUSE NFM observations unveil a tuning-fork ionised gas morphology

TL;DR

This study uses high-resolution MUSE NFM observations to reveal a detailed, tuning-fork shaped ionised gas outflow in the Circinus galaxy, providing insights into AGN-driven outflow morphology and interactions with the interstellar medium.

Contribution

First high-resolution ground-based optical observations uncover a complex, tuning-fork shaped ionised gas outflow in Circinus, linking small-scale outflow structures to larger-scale filaments.

Findings

Outflow extends up to 30 pc with a tuning-fork morphology.

Interaction with dense ISM clumps shapes the outflow structure.

Ionised outflows are unlikely to regulate star formation at 100 pc scales.

Abstract

We present the ionised gas outflow morphology in the Circinus galaxy using the Narrow Field Mode (NFM) of the MUSE instrument on board the Very Large Telescope (VLT). The NFM observations provide a spatial resolution of $\sim$0.1", corresponding to a physical scale of $\sim$2 pc, one of the highest spatial resolution achievable using ground-based AO-assisted observations in the optical wavelengths. The MUSE observations reveal a collimated clumpy outflow profile originating near the AGN location and extending up to 1.5" ($\sim$30 pc) in the NW direction. The collimated structure then fragments into two filaments, giving the entire outflowing gas a ``tuning-fork'' morphology. These structures remain undetected in the lower spatial resolution MUSE Wide Field Mode data. We explain the origin of this tuning-fork structure to the interaction of the outflow with a dense clump in the interstellar medium (ISM) as the outflow propagates outward. The origin of the collimated structure itself could be from jet-ISM interactions on small scales. These observations also provide evidence to the origin of the ionised gas filaments previously observed in the Circinus galaxy out to kiloparsec scales. We find instantaneous and time-averaged mass outflow rates of 10$^{-2}$ M$_{\odot}$ yr$^{-1}$ and 10$^{-4}$ M$_{\odot}$ yr$^{-1}$, respectively. Based on the star formation rate in the Circinus galaxy reported in the literature, the observed ionised outflows are not expected to regulate star formation within the $\sim$100 pc scales probed by the NFM data.