MICONIC: JWST/MIRI-MRS reveals heavily reprocessed polycyclic aromatic hydrocarbons in the circumnuclear disc of Centaurus A

¹ Department of Physics and Astronomy, Universiteit Gent, Proeftuinstraat 86 N3, B-9000, Ghent, Belgium
² Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001, Leuven, Belgium
³ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98bis bd Arago, 75014, Paris, France
⁴ Institut Universitaire de France, Ministère de l’Education Nationale, de l’Enseignement Supérieur et de la Recherche, 1 rue Descartes, 75231, Paris Cedex 05, France
⁵ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, E-28692, Villanueva de la Cañada, Madrid, Spain
⁶ Telespazio UK for the European Space Agency (ESA), ESAC, Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada, Spain
⁷ European Space Agency, c/o Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA
⁸ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill Edinburgh, EH9 3HJ, Scotland, UK
⁹ Observatorio Astronómico Nacional (OAN-IGN)-Observatorio de Madrid, Alfonso XII, 3, 28014, Madrid, Spain
¹⁰ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, Leiden, The Netherlands
¹¹ Dept. of Astrophysics, University of Vienna, Türkenschanzstr. 17, A-1180, Vienna, Austria
¹² ETH Zürich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Str. 27, 8093, Zürich, Switzerland
¹³ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191, Gif-Sur-Yvette, France
¹⁴ Department of Physics, University of Oxford, Keble Road, Oxford, OX1 3RH, UK
¹⁵ Department of Physics, University of California, San Diego, California, 92093, USA
¹⁶ Physikalisches Institut der Universität zu Kïln, Zülpicher Str. 77, D-50937, Köln, Germany; Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, D-53121, Bonn, Germany
¹⁷ Department of Astronomy, Stockholm University, The Oskar Klein Centre, AlbaNova, SE-106 91, Stockholm, Sweden
¹⁸ LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 92190, Meudon, France
¹⁹ Max Planck Institute for Astronomy, Königstuhl 17, 69117, Heidelberg, Germany
²⁰ Centre for Extragalactic Astronomy, Durham University, South Road, Durham, DH1 3LE, UK

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Received: 31 December 2025
Accepted: 23 March 2026

Abstract

Context. Polycyclic aromatic hydrocarbons (PAHs) constitute essential components of dust in galaxies and have a fundamental role in the physics of the interstellar medium (ISM). The impact of AGN feedback on these molecules is still under debate.

Aims. We aim to present a detailed analysis of the spatially resolved properties of PAHs in the central 7″ × 12″ (∼100 × 200 pc²) of Centaurus A (Cen A). We used the JWST/MIRI-MRS observations at λ ∼ 5 − 28 μm taken as part of the MIRI European consortium’s Guaranteed Time Observation (GTO) program MICONIC, with angular resolution between 0.35″ and 1″ (∼6 − 17 pc).

Methods. We derived PAH moment-zero maps through local continuum subtraction and extracted one-dimensional spectra in five regions of interest, including the nucleus, the circumnuclear disc, and a region characterised by a prominent deficiency in PAH emission. We decomposed the spectra into continuum, emission lines, and PAHs, from which we extracted PAH intensities and equivalent widths (EWs).

Results. Polycyclic aromatic hydrocarbon emission is predominantly distributed in a ring-like structure with localised intensity enhancements, at a radius of ∼40 pc from the active nucleus. Towards the north-west we observe a distinct PAH-deficient area, roughly perpendicular to the jet axis and coincident with enhanced ionised-gas velocity dispersion as well as inflowing warm and cold molecular streamers. The PAH 11.3/7.7 μm and 6.2/7.7 μm intensity ratios exceed model predictions for peri-condensed PAHs, suggesting heavily reprocessed populations characterised by more open and irregular molecular structures. PAH 11.3/12.7 μm ratios point to a prevalence of solo over duo or trio hydrogen sites, consistent with a non-negligible degree of dehydrogenation, particularly within the PAH-deficient region, where shock-driven erosion may play a major role. We measured the largest EWs in the PAH ring, whereas reduced values in the PAH-deficient region likely reflect partial destruction by shocks; in the nucleus, the small EWs are largely attributable to continuum dilution.