PAHSPECS: JWST/MIRI Spectroscopy of PAHs at Cosmic Noon
Abstract
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 z~1-2 (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 z~1. 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.
Related
- PAHSPECS: Polycyclic aromatic hydrocarbon properties at cosmic noon with JWST/MIRI MRS
- PDRs4All XXIII. JWST-MIRI template spectra of PAHs in the Orion Bar obtained with blind signal separation
- Resolved Dust in z≈1 Galaxies with JWST/MIRI MRS: Survey Description and First View on PAHs, Mid-IR Atomic Emission, and Warm H2
- JWST Observations of Starbursts: The Motion of Dust—PAH Kinematics of M82 and NGC 253 with JWST/MIRI Spectroscopy
- JWST Observations of Starbursts: The motion of dust - PAH kinematics of M82 and NGC 253 with JWST/MIRI spectroscopy
BibTeX
@misc{shivaei2026pahspecs,
title = {{PAHSPECS: JWST/MIRI Spectroscopy of PAHs at Cosmic Noon}},
author = {Irene Shivaei and Tanio Díaz Santos and Leindert Boogaard and Karin Sandstrom and Cristina Lofaro and Fergus Donnan and Pablo González and Roman Fernández Aránda and Javier Álvarez Márquez and Manuel Aravena and Roberto Decarli and Frédéric Galliano and Hanae Inami and Göran Östlin and Gergö Popping and Fabian Walter and Paul van der Wer},
howpublished = {Astronomy \& Astrophysics - A\&A},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.29955},
eprint = {2609.29955},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05779094v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - PAHSPECS: JWST/MIRI Spectroscopy of PAHs at Cosmic Noon
AU - Irene Shivaei
AU - Tanio Díaz Santos
AU - Leindert Boogaard
AU - Karin Sandstrom
AU - Cristina Lofaro
AU - Fergus Donnan
AU - Pablo González
AU - Roman Fernández Aránda
AU - Javier Álvarez Márquez
AU - Manuel Aravena
AU - Roberto Decarli
AU - Frédéric Galliano
AU - Hanae Inami
AU - Göran Östlin
AU - Gergö Popping
AU - Fabian Walter
AU - Paul van der Wer
PY - 2026
DA - 2026/09/24
PB - Astronomy & Astrophysics - A&A
DO - 10.48550/arxiv.2609.29955
UR - https://hal.science/hal-05779094v1
AB - 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 z~1-2 (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 z~1. 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 L_PAH/L_IR 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.
SN - 0004-6361
SN - 1432-0746
ER -