![Ratio maps involving the PAH7.7 feature and the F1500W synthetic photometry applied to the MRS cubes for ASPECS galaxies. The first row of panels shows the maps of the total PAH7.7 feature to the synthetic F1500W photometry. Ratios above 1 are possible because the wings of the PAH feature extend well beyond the filter (see text for details and Donnan et al. 2026b). The second row of panels is the fraction of PAH7.7 feature within the F1500W filter to the synthetic F1500W photometry. The third row of panels is the same as the second but for the fraction of continuum emission within the F1500W to the synthetic F1500W photometry -- [astro-ph.GA]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/09/PAHSPECS.png?fit=1200%2C673&ssl=1)
[astro-ph.GA] The physical conditions of the interstellar medium (ISM) are thought to differ greatly at high redshifts compared to local galaxies. Polycyclic aromatic hydrocarbons (PAHs) are key ISM constituents, mediating the heating and cooling of gas in photo-dissociation regions.
However, PAHs are unexplored in main-sequence (MS) galaxies at z1-2 (cosmic noon), limiting our view of the ISM’s thermal and chemical balance. We present the PAH Spectroscopic Survey (PAHSPECS) JWST program, the first MIRI/MRS survey of the 3.3, 6.2, 7.7, 8.6 and 11.3μm PAH features in MS galaxies at z1.
The five targets come from the deep ALMA CO and continuum flux-limited sample in the HUDF. We detect the 6.2, 7.7 and 11.3μm PAHs in all galaxies, and the 3.3μm feature in only two. Spectral energy distribution (SED) fitting to broad-band mid-IR photometry recovers the 6.2 and 7.7μm PAH luminosities derived from spectral decomposition of the MRS spectra to within ~25% accuracy.
However, the 3.3 and 11.3μm features are overestimated by ~50% (up to 3-5x). Spatially resolved maps of ASPECS-6, the most extended source, show variations of the 7.7μm PAH contribution to the MIRI F1500W flux, suggesting that while photometry can infer PAH luminosity accurately, IFU spectroscopy is necessary to study variations in PAH ratios and characterize galaxy dust properties.
The PAH fraction of the total dust mass from photometric SED modeling roughly agrees with the LPAH/LIR ratio measured from spectroscopy, but the correlation is not as tight as models predict.
On average, PAHSPECS galaxies show an excess in 6.2μm equivalent width relative to nearby dusty luminous systems, but lower 3.3μm equivalent widths than local systems, similar to higher-mass starbursts at z~1-3. This points to differential changes in the size distributions of neutral and ionized PAHs in cosmic noon galaxies.
Multi-wavelength cutouts of PAHSPECS galaxies. , from left to right, RGB from JWST/NIRCam F444W, JWST/NIRCam F277W, and HST/WFC3 F160W filters (JADES), JWST/MIRI F1500W (Section 2.2.3), and JWST/MRS continuum-subtracted emission line maps of PAH 3.3, 6.2, 7.7, and 11.3 µm features (Donnan et al. 2026b). The four PAH maps in each row share the same color scale so that the relative strengths of the different PAH features can be compared within each source (the color scale is not shared between rows). — [astro-ph.GA]
Irene Shivaei, Tanio Díaz Santos, Leindert A. Boogaard, Karin Sandstrom, Cristina Lofaro, Fergus R. Donnan, Pablo G. Pérez González, Roman Fernández Aránda, Javier Álvarez Márquez, Manuel Aravena, Roberto Decarli, Frédéric Galliano, Hanae Inami, Göran Östlin, Gergö Popping, Fabian Walter, Paul van der Wer
Comments: Submitted to A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2609.29955 [astro-ph.GA] (or arXiv:2609.29955v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2609.29955
Focus to learn more
Submission history
From: Irene Shivaei
[v1] Thu, 24 Sep 2026 15:12:23 UTC (3,851 KB)
https://arxiv.org/abs/2609.29955
Astrobiology, Astrochemistry,
