A Full-Sky SPHEREx Map of Integrated 3.3 and 3.4 μm PAH Emission
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium and are among its smallest carbonaceous grains. Their infrared emission bands trace this small-grain population together with the interstellar radiation field that excites it, and are widely used to diagnose photodissociation regions, dust processing and star formation. We present full-sky maps of the integrated radiance of the 3.3 μm aromatic C-H stretch and the adjacent 3.4-3.5 μm aliphatic complex, from SPHEREx QR2 Level-2 data. Existing all-sky PAH tracers are broadband, so the band emission can only be inferred as an excess over stellar and continuum emission; SPHEREx samples the spectrum finely enough for the bands to be fitted directly. We mask flagged detector pixels, subtract the per-pixel zodiacal-light model, subtract point sources with an empirically derived PSF, and coadd the results into inverse-variance-weighted HEALPix maps at 2.6' FWHM and Nside=4096 in 102 narrowband channels across Detector 4 (2.42-3.82 μm). At every sky pixel we fit a continuum and the two bands. The combined band radiance is the primary product; its decomposition into the aromatic and aliphatic components is released alongside it as an estimate, with its modelling systematic stated. These are the first full-sky maps of PAH band emission, resolving the 3.3 and 3.4-3.5 μm bands spectrally, and the first full-sky PAH maps from SPHEREx to be released. Because the 3.3 μm band is emitted preferentially by the smallest PAHs, the maps trace directly a grain population, including the candidate carriers of anomalous microwave emission, that broadband PAH proxies reach only indirectly. The maps and their associated products, including a reliability mask, are publicly available with an explanatory supplement at https://research.iac.es/proyecto/radioforegroundsplus/pages/data-products/spherex-pahs.php.
Related
- SPHEREx 3.3 Micron Aromatic Emission in the Magellanic Clouds: Separating Dust Column, Excitation, and Environmental Suppression
- Empirical Near-Infrared Spectral Templates from SPHEREx: Disentangling AGN and Host-Galaxy Emission
- SPHEREx 3.3 Micron Aromatic Emission in the Magellanic Clouds: Separating Dust Column, Excitation, and Environmental Suppression
- The shell around VY Canis Majoris in SPHEREx is likely an artifact
- Detection of new Galactic Wolf-Rayet stars with SPHEREx
BibTeX
@misc{cepedaarroita2026fullsky,
title = {{A Full-Sky SPHEREx Map of Integrated 3.3 and 3.4 μm PAH Emission}},
author = {Roke Cepeda-Arroita and Clive Dickinson and J. Alberto Rubiño-Martín and Ricardo T. Génova-Santos and Gabriel A. Hoerning and Stuart E. Harper and Debabrata Adak},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.37878},
eprint = {2609.37878},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.37878},
}
RIS
TY - UNPB
TI - A Full-Sky SPHEREx Map of Integrated 3.3 and 3.4 μm PAH Emission
AU - Roke Cepeda-Arroita
AU - Clive Dickinson
AU - J. Alberto Rubiño-Martín
AU - Ricardo T. Génova-Santos
AU - Gabriel A. Hoerning
AU - Stuart E. Harper
AU - Debabrata Adak
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2609.37878
UR - https://arxiv.org/abs/2609.37878
AB - Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium and are among its smallest carbonaceous grains. Their infrared emission bands trace this small-grain population together with the interstellar radiation field that excites it, and are widely used to diagnose photodissociation regions, dust processing and star formation. We present full-sky maps of the integrated radiance of the 3.3 μm aromatic C-H stretch and the adjacent 3.4-3.5 μm aliphatic complex, from SPHEREx QR2 Level-2 data. Existing all-sky PAH tracers are broadband, so the band emission can only be inferred as an excess over stellar and continuum emission; SPHEREx samples the spectrum finely enough for the bands to be fitted directly. We mask flagged detector pixels, subtract the per-pixel zodiacal-light model, subtract point sources with an empirically derived PSF, and coadd the results into inverse-variance-weighted HEALPix maps at 2.6' FWHM and Nside=4096 in 102 narrowband channels across Detector 4 (2.42-3.82 μm). At every sky pixel we fit a continuum and the two bands. The combined band radiance is the primary product; its decomposition into the aromatic and aliphatic components is released alongside it as an estimate, with its modelling systematic stated. These are the first full-sky maps of PAH band emission, resolving the 3.3 and 3.4-3.5 μm bands spectrally, and the first full-sky PAH maps from SPHEREx to be released. Because the 3.3 μm band is emitted preferentially by the smallest PAHs, the maps trace directly a grain population, including the candidate carriers of anomalous microwave emission, that broadband PAH proxies reach only indirectly. The maps and their associated products, including a reliability mask, are publicly available with an explanatory supplement at https://research.iac.es/proyecto/radioforegroundsplus/pages/data-products/spherex-pahs.php.
ER -