MICONIC: The multiphase circumnuclear region of Centaurus A as seen with JWST/MIRI MRS observations

I. Spectral inventory and properties of the warm molecular disk

¹ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98bis bd Arago, 75014 Paris, France
² SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht, The Netherlands
³ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, Leiden, The Netherlands
⁴ Observatoire de Paris, PSL University, Sorbonne Université, LUX, 75014 Paris, France
⁵ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, E-28692 Villanueva de la Cañada, Madrid, Spain
⁶ Department of Physics and Astronomy, Universiteit Gent, Proeftuinstraat 86 N3, B-9000 Ghent, Belgium
⁷ Telespazio UK for the European Space Agency (ESA), ESAC, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Spain
⁸ European Space Agency, c/o Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁹ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir km 4, Torrejón de Ardoz, 28850 Madrid, Spain
¹⁰ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill Edinburgh, EH9 3HJ, Scotland, UK
¹¹ Centre for Extragalactic Astronomy, Durham University, South Road, Durham DH1 3LE, UK
¹² Observatorio Astronómico Nacional (OAN-IGN)-Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain
¹³ Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
¹⁴ Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, D-53121 Bonn, Germany
¹⁵ Department of Astronomy, Stockholm University, The Oskar Klein Centre, AlbaNova SE-106 91, Stockholm, Sweden
¹⁶ LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 92190 Meudon, France
¹⁷ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁸ Departamento de Física, CCNE, Universidade Federal de Santa Maria, Av. Roraima 1000, 97105-900 Santa Maria, RS, Brazil
¹⁹ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir km 4, Torrejón de Ardoz, E-28850 Madrid, Spain
²⁰ Dept. of Astrophysics, University of Vienna, Türkenschanzstr 17, A-1180 Vienna, Austria
²¹ ETH Zürich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Str. 27, 8093 Zürich, Switzerland
²² ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands

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Received: 2 December 2025
Accepted: 18 May 2026

Abstract

Context. Supermassive black holes power active galactic nuclei (AGNs), injecting energy that may regulate accretion and shapes host galaxies. High-resolution observations of circumnuclear gas and dust are essential to understanding these processes.

Aims. We aim to investigate the morphology, excitation, and kinematics of warm molecular hydrogen (H₂) in the inner circumnuclear disk of Centaurus A, the nearest radio galaxy.

Methods. We present JWST/MIRI MRS integral-field spectroscopy of the central 170 × 100 pc² at 0.3″–0.7″ (5–12 pc) resolution, focusing on pure rotational H₂ lines. The spectra exhibit a strong nuclear continuum, and bright H₂ lines from S(1) to S(8), including the first S(8) detection in Centaurus A. The lines are optically thin in the nucleus, enabling maps of temperature, column density, and ortho-to-para ratio from spaxel-level excitation diagram fitting.

Results. Warm H₂ shows a complex morphology, dominating the central region where CO emission is weak or undetected. Low-excitation H₂ lines trace an inhomogeneous ring with a 20-pc radius cavity aligned with the jet’s near side, suggesting that the jet affects the morphology of the molecular disk. Higher excitation lines form a filamentary structure around the AGN. Kinematics are primarily rotational with an S-shaped distortion, indicating noncircular motions or a warped disk. A coherent, low-dispersion (∼70 km s⁻¹) streamer spirals inward. A power-law temperature distribution yields a warm (100–2000 K) H₂ mass of (5.6 ± 1.4)×10⁵ M_⊙ and a dynamical mass of 5 × 10⁸ M_⊙ within 100 pc. Shock excitation is supported by enhanced H₂/continuum and H₂/PAH ratios, elevated [Ne III]/[Ne II], and sub-equilibrium ortho-to-para ratios (1.6–2.4).

Conclusions. Turbulent dissipation can balance the observed H₂ cooling and likely dominates heating beyond 30 pc. In the inner 100 pc of Centaurus A, AGN feeding and feedback are linked: shocks excite H₂, regulate the gas temperature, and prevent cooling below 100 K, explaining the weak CO emission and lack of a massive outflow. These shocks may drive angular-momentum loss and help fuel the nucleus.