Carbonaceous dust processing in the merger galaxy II Zw 096: High-resolution polycyclic aromatic hydrocarbon diagnostics with JWST

Journal article, 2026

Context. Galaxy mergers drive intense radiation environments that fundamentally alter interstellar dust properties through photo-destruction and thermal processing. The luminous infrared galaxy II Zw 096 presents several distinctive regions, including starburst clumps and a proposed buried Active galactic nucleus (AGN) in region D1, making it an ideal laboratory for studying dust evolution under extreme conditions. Aims. This work aims to determine the carbonaceous dust properties across II Zw 096 by characterizing the spatial variations in carbonaceous feature ratios and to investigate how intense radiation fields process carbonaceous dust grains, using the relationship between dust processing signatures and traditional radiation field diagnostics. Methods. Using JWST NIRSpec IFU and MIRI MRS, carbonaceous features were observed and analyzed using the Continuum and Feature Extraction tool (CAFE) with 61 carbonaceous features from the PDRs4all project and new absorption features for ice and crystalline silicates. We analyze spatial variations in carbonaceous feature ratios at multiple resolutions (0.281 '', 0.787 '', and 0.961 '') to trace dust composition and grain-size distribution. The 3.4/3.3 & micro;m ratio probes aliphatic versus aromatic content, while the 11.3/3.3 & micro;m ratio diagnoses grain-size distribution. Results. The 3.4/3.3 & micro;m ratio spans between 0.056-0.148, with the lowest values near the proposed AGN (D1) and starburst clumps (C0, D0), indicating preferential destruction of C-H bonds connected to aliphatic structures in highly irradiated environments. The 11.3/3.3 & micro;m ratio varies from 0.334 to similar to 2.348 in D1. Both polycyclic aromatic hydrocarbon (PAH) ratios show no clear correlation with [Ne III]/[Ne II], suggesting ionization diagnostics break down either in extreme merger environments or as an effect of tracing different interstellar medium (ISM) phases and radiation-field regimes in this highly obscure merger environment. We detect water ice (3.1 & micro;m), CO2 ice (4.27 & micro;m), and crystalline silicates (11.1 & micro;m) with spatial distributions anti-correlating with carbonaceous processing signatures. Conclusions. Spatial resolution critically affects dust diagnostics: the 3.4/3.3 & micro;m dynamic range doubles when increasing the resolution from 0.961 '' to 0.281 '', demonstrating that apparent uniformity at low resolution masks significant variations in compact regions undergoing intense dust processing. Multiple coherent diagnostics point to intense dust processing, such as photo-destruction of the smallest nanograins and aromatisation, consistent with a buried AGN in D1, although definitive confirmation remains elusive.