JWST/MIRI-MRS View of the Metal-poor Galaxy CGCG 007-025: The Spatial Location of Polycyclic Aromatic Hydrocarbons and Very Highly Ionized Gas

Abstract Polycyclic aromatic hydrocarbons (PAHs) are key diagnostics of the physical conditions in the interstellar medium and are widely used to trace star formation in the mid-infrared (mid-IR). The relative strengths of mid-IR PAH features (e.g., 6.2, 7.7, and 11.3 μ m) are sensitive to both the size and ionization state of the molecules and can be strongly influenced by the local radiation field. However, at low metallicities ( Z < 0.2 Z ⊙ ), detecting PAHs remains notoriously difficult, likely reflecting a combination of suppressed formation and enhanced destruction mechanisms. We present new JWST/MIRI Medium Resolution Spectroscopy (MRS) observations of the metal-poor ( Z ∼ 0.1 Z ⊙ ) dwarf galaxy CGCG 007-025. We confirm the tentative PAH detection previously reported from Spitzer data and, for the first time, identify a compact (∼50 pc) PAH-emitting region nearly cospatial with the newly detected [Ne v ] (Ionization potential (I.P.) ∼ 97 eV) emission and the galaxy’s most metal-poor, strongly star-forming region. The PAH 11.3 μ m and PAH 12.7 μ m features are detected, while no emission is found from other typically brighter features, suggesting a PAH population dominated by large, neutral molecules resilient to hard ionizing fields. When compared with models, mid-IR line ratios involving [Ne iii ], [O iv ], and [Ne v ] can only be reproduced by a combination of star formation and AGN ionization, with the latter contributing 4%–8%. The [O iv ] and [Ne v ] luminosities exceed what massive stars or shocks can produce, highlighting a puzzling scenario in line with recent JWST observations of similar galaxies. This work provides a crucial reference for studying the physical conditions of the dust and star formation in low-metallicity starburst regions, environments typical of the early Universe.