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arXiv · 2609.37878

A Full-Sky SPHEREx Map of Integrated 3.3 and 3.4 μm PAH Emission

Roke Cepeda-Arroita·Clive Dickinson·J. Alberto Rubiño-Martín·Ricardo T. Génova-Santos·Gabriel A. Hoerning·Stuart E. Harper·Debabrata Adak
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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 $μ$m aromatic C-H stretch and the adjacent 3.4-3.5 $μ$m 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 $μ$m). 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 $μ$m bands spectrally, and the first full-sky PAH maps from SPHEREx to be released. Because the 3.3 $μ$m 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.

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Roke Cepeda-Arroita, Clive Dickinson, J. Alberto Rubiño-Martín, Ricardo T. Génova-Santos, Gabriel A. Hoerning, Stuart E. Harper, Debabrata Adak. 2026-09-29. A Full-Sky SPHEREx Map of Integrated 3.3 and 3.4 μm PAH Emission. https://arxiv.org/abs/2609.37878

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