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

Abstract

We present the ionized gas outflow morphology in the Circinus galaxy using the narrow-field mode (NFM) of the Multi Unit Spectroscopic Explorer (MUSE) instrument onboard the Very Large Telescope (VLT). The NFM observations provide a spatial resolution of ∼0.1 arcsec, corresponding to a physical scale of ∼2 pc, one of the highest spatial resolution achievable using ground-based adaptive optics-assisted observations in the optical wavelengths. The MUSE observations reveal a collimated clumpy outflow profile originating near the active galactic nucleus (AGN) location and extending up to 1.5 arcsec (∼30 pc) in the north-west 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 outwards. 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 ionized gas filaments previously observed in the Circinus galaxy out to kiloparsec scales. We find instantaneous and time-averaged mass outflow rates of 10-2 and 10-4 M⊙ yr-1, respectively. Based on the star formation rate in the Circinus galaxy reported in the literature, the observed ionized outflows are not expected to regulate star formation within the ∼100 pc scales probed by the NFM data.

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