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Survival of very small carbonaceous dust grains in the inner circumgalactic medium of NGC 891 from JWST/MIRI MRS

Jérémy ChastenetDepartment of Physics and Astronomy, Universiteit GentIlse De LoozeDepartment of Physics and Astronomy, Universiteit GentKarl D. GordonDepartment of Physics and Astronomy, Universiteit GentSuzanne C. MaddenAstrophysique, Instrumentation et ModélisationM. RelañoDept. Fisica Teorica y del CosmosKarin SandströmDepartment of Astronomy & Astrophysics, University of California, San DiegoDries Van De PutteDepartment of Physics & Astronomy, The University of Western OntarioMaarten BaesDepartment of Physics and Astronomy, Universiteit GentSimone BianchiINAF – Osservatorio Astrofisico di ArcetriAlberto D. BolattoDepartment of Astronomy and Joint Space-Science Institute, University of MarylandViviana CasasolaINAF – Istituto di RadioastronomiaDaniel A. DaleDepartment of Physics and Astronomy, University of WyomingSara DuvalRitter Astrophysical Research Center, University of ToledoJacopo FritzInstituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de MéxicoF. GallianoCEA Paris-SaclaySimon C. O. GloverUniversität Heidelberg, Zentrum für Astronomie, Institut für Theoretische AstrophysikS. KatsioliNational Observatory of Athens, IAASARSVasileios KatsisPhysique des Interactions Ioniques et Moléculaires, CNRS, Aix Marseille UniversitéFlorian KirchschlagerDepartment of Physics and Astronomy, Universiteit GentRalf S. KlessenUniversität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches RechnenRebecca C. LevySpace Telescope Science InstituteSharon E. MeidtDepartment of Physics and Astronomy, Universiteit GentAleksandr V. MosenkovDepartment of Physics and Astronomy, N283 ESC, Brigham Young UniversityKentaro NagamineDepartment of Physics & Astronomy, University of Nevada, Las VegasL. PantoniDepartment of Physics and Astronomy, Universiteit GentHelena M. RichiePhysics and Astronomy Department, University of PittsburghStefanie WalchUniversität zu Köln, I. Physikalisches InstitutThomas G. WilliamsSub-department of Astrophysics, Department of Physics, University of OxfordEmanuele M. XilourisNational Observatory of Athens, IAASARS

2026

ABI

Annotatsiya

We present new spectroscopic observations of the inner circumgalactic medium (CGM) of NGC 891 taken with the Mid-Infrared Imager/Medium Resolution Spectroscopy instrument on board JWST, in four positions: two near the bulge and two at galactocentric radii ( r ) of ∼1.5, 4.7 kpc. Each pair of pointings has one position along the minor axis ( h ) at ∼0.5 kpc and one at ∼1 kpc away from the mid-plane. We analysed 1D spectra and 3D cubes using the dust emission model PAHFIT to extract properties of typical mid-IR features. These spectra reveal that the earlier reported mid-IR emission out to 4 kpc is dominated by the emission of polycyclic aromatic hydrocarbons (PAHs), and not hot dust continuum, thus providing direct evidence of the survival of PAHs in the inner CGM of NGC 891. Comparing PAH band ratios with other environments (Orion, M51), it is obvious that the 11.2 μm PAH feature – and not the usual 7.7 μm – dominates in NGC 891, which seems to imply the presence of more neutral, large PAHs in the CGM. Overall, PAH-to-continuum ratios show little variations with scale-height and radius in NGC 891, which suggests little PAH processing. However, we do see a decrease in the PAH feature strengths with the [Ne III ]/[Ne II ] ratio, which points to elevated dust processing with increased radiation field hardness. We also confirm a tight correlation between H 2 and PAH features, which suggests that the two tracers must be co-spatial, and hence implies that PAH emission predominantly arises from cool dense parts of cloudlets entrained in galactic outflows. Finally, we report the clear detection of a previously unidentified PAH feature at 16.72 μm.

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DOI: 10.1051/0004-6361/202558757

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