Torus feeding and outflow launching in the active nucleus of the Circinus galaxy

¹ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
² European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
³ Institute ASTRON, Netherlands Institute for Radio Astronomy, NL-7991 PD Dwingeloo, The Netherlands
⁴ Instituto de Estudios Astrofísicos, Universidad Diego Portales, Av. Ejírcito Libertador 441, Santiago, Chile
⁵ School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023, People’s Republic of China
⁶ School of Astronomy and Space Science, Nanjing University, Nanjing 210093, China
⁷ Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, China

^⋆ Corresponding author: goesaert@strw.leidenuniv.nl

Received: 16 May 2025
Accepted: 23 September 2025

Abstract

Context. Most active galactic nuclei (AGNs) are believed to be surrounded by a dusty molecular torus on the parsec scale, which is often embedded within a larger circumnuclear disc (CND). Active galactic nuclei are fuelled by the inward transport of material through these structures and can launch multi-phase outflows that influence the host galaxy through AGN feedback.

Aims. We use the Circinus galaxy as a nearby laboratory to investigate the physical mechanisms responsible for feeding the torus and launching a multi-phase outflow in this Seyfert-type AGN, as these mechanisms remain poorly understood.

Methods. We analysed observations from the Atacama Large Millimeter/submillimeter Array of the Circinus nucleus at angular resolutions down to 13 mas (0.25 pc). We traced dust and the ionised outflow using 86 − 665 GHz continuum emission and studied the morphology and kinematics of the molecular gas using the HCO⁺(3-2), HCO⁺(4-3), HCN(3-2), HCN(4-3), and CO(3-2) transitions.

Results. We find that the Circinus CND hosts molecular and dusty spiral arms, two of which connect directly to the torus. We detect inward mass transport along these structures and argue that the non-axisymmetric potential generated by these arms is the mechanism responsible for fuelling the torus. We estimate a feeding rate of 0.3 − 7.5 M_⊙ yr⁻¹, implying that over 88% of the inflowing material is expelled in a multi-phase outflow before reaching the accretion disc. The inferred feeding timescale (t_{feed,  torus} = 120 kyr − 2.7 Myr) suggests that variability in AGN activity may be driven by changes in torus feeding. On parsec scales, the ionised outflow is traced by optically thin free-free emission. The outflow is stratified, with a slightly wider opening angle in the molecular phase than in the dusty and ionised components. The ionised outflow is launched or collimated by a warped accretion disc at a radius of r ∼ 0.16 pc, and its geometry requires an anisotropic launching mechanism.