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

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 pc 2 ) 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.