Proyecto de Investigación: AYUDAS RAMÓN Y CAJAL 2021
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ID
RYC2021-033094-I
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Publicaciones
The PAH 3.4 micron feature as a tracer of shielding in the Orion Bar and NGC 6240
(Royal Astronomical Society, 2025-11-18) Thatte, Niranjan; Rigopoulou, Dimitra; Donnan, Fergus; García-Bernete, Ismael; Pereira Santaella, Miguel; Draine, B.; Veenema, Oscar; Kerkeni, Boutheïna; Alonso-Herrero, Almudena; Hermosa Muñoz, Laura; Speranza, G.; Science and Technology Facilities Council (STFC); Comunidad de Madrid; University of Oxford; Agencia Estatal de Investigación (España)
We have carried out a detailed analysis of the 3.4 μm spectral feature arising from Polycyclic Aromatic Hydrocarbons (PAH), using James Webb Space Telescope archival data. For the first time in an external galaxy (NGC 6240), we have identified two distinct spectral components of the PAH 3.4 μm feature: a shorter wavelength component at 3.395 μm, which we attribute to short aliphatic chains tightly attached to the aromatic rings of the PAH molecules; and a longer wavelength feature at 3.405 μm that arises from longer, more fragile, aliphatic chains that are weakly attached to the parent PAH molecule. These longer chains are more easily destroyed by far-ultraviolet photons (>5 eV) and PAH thermal emission only occurs where PAH molecules are shielded from more energetic photons by dense molecular gas. We see a very strong correlation in the morphology of the PAH 3.395 μm feature with the PAH 3.3 μm emission, the latter arising from robust aromatic PAH molecules. We also see an equally strong correlation between the PAH 3.405 μm morphology and the warm molecular gas, as traced by H2 vibrational lines. We show that the flux ratio PAH 3.395/PAH 3.405 < 0.3 corresponds strongly to regions where the PAH molecules are shielded by dense molecular gas, so that only modestly energetic UV photons penetrate to excite the PAHs. Our work shows that PAH 3.405 μm and PAH 3.395 μm emission features can provide robust diagnostics of the physical conditions of the interstellar medium in external galaxies, and can be used to quantify the energies of the photon field penetrating molecular clouds.
GATOS – XI. Excess dust heating in the narrow-line regions of nearby AGN revealed with JWST/MIRI
(Blackwell Publishing, 2026-01-26) Haidar, Houda; Rosario, David J.; García-Bernete, Ismael; Alonso-Herrero, Almudena; Audibert, Anelise; Campbell, Steph; Harrison, Chris; Costa, Tiago; Hermosa Muñoz, Laura; Combes, Françoise; Rigopoulou, Dimitra; Ricci, Claudio; Ramos Almeida, Cristina; Bellocchi, Enrica; Boorman, Peter; Bunker, Andrew; Davies, Richard; Delaney, Daniel; Díaz Santos, Tanio; Esposito, Federico; Fawcett, Victoria; Gandhi, Poshak; García-Burillo, Santiago; González-Martín, Omaira; Hicks, E.K.S.; Hönig, Sebastian F.; Labiano, Alvaro; Levenson, Nancy A.; Lopez-Rodriguez, Enrique; Packham, Chris; Pereira-Santaella, Miguel; Riffel, Rogemar A.; Rodríguez Ardila, Alberto; Schneider, John; Thomas Shimizu, Taro; Stalevski, Marko; Villar Martín, Montserrat; Ward, Martin; Zhang, Lulu; Leeds, Gillian; Donnan, Fergus; European Commission (EC); Comunidad de Madrid; Ministerio de Ciencia e Innovación (MICINN); Swiss National Science Foundation (SNSF); Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT); Ministry of Education, Science and Technological Development of the Republic of Serbia; Agencia Estatal de Investigación (AEI); European Research Council (ERC); UK Research and Innovation (UKRI); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Foundation of Rio Grande do Sul State for Research Support (FAPERGS)
We present James Webb Space Telescope/Mid-Infrared Instrument imaging of eight nearby active galactic nuclei (AGN) from the GATOS (Galactic Activity, Torus, and Outflow Survey) survey to investigate the physical conditions of extended dust in their narrow-line regions (NLRs). In four galaxies (ESO 428–G14, NGC 4388, NGC 3081, and NGC 5728), we detect spatially resolved dust structures extending ∼100–200 pc along the NLR. In these systems, we find a strong link between the morphology of the dust, the radio ejecta, and the coronal [Sivi] emission, implying that dust carries imprints of the processes shaping the NLR. Using spatially resolved spectral energy distributions, we show that dust in the NLR has systematically steeper slopes than star-forming clumps. This dust emits at temperatures in the range $150 \text{-} 220\, \rm K$, at a distance of ∼150 pc from the nucleus. Using simple models, we show that, even under optimistic assumptions of grain size and AGN luminosity, the excess mid-infrared emission cannot be explained by AGN illumination alone. We interpret this excess heating as in situ. We show that shocks with velocities v ∼ 200 - 400 km s in dense gas can close this gap, and in some cases even account for the total observed emission. This, combined with multiple lines of evidence for shocks in these regions, supports a scenario in which shocks not only coexist with dust but may be playing a key role in heating it. Our findings reveal shocks may be an important and previously overlooked driver of extended dust emission in the central hundreds of parsecs in AGN.
