![The per-tile processing chain, applied to the Detector-4 tile of Fig. 1. (a) After flag masking and zodiacal-light subtraction, the input to the stellar subtraction. (b) After fitting and subtracting the empirical PSF at every catalogued source above the magnitude limit, with the saturated cores of the brightest stars masked. (c) After the median filter and the Gaussian smoothing to 2.6 ′ , which is what is coadded into the HEALPix maps. All three panels share a single histogram-equalised colour scale. -- [astro-ph.GA]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/10/A-Full-Sky.png?fit=1200%2C597&ssl=1)
[astro-ph.GA] 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.
Roke Cepeda-Arroita, Clive Dickinson, J. Alberto Rubiño-Martín, Ricardo T. Génova-Santos, Gabriel A. Hoerning, Stuart E. Harper, Debabrata Adak
Comments: 19 pages, 9 figures, submitted to A&A. Maps and explanatory supplement: this https URL
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2609.37878 [astro-ph.GA] (or arXiv:2609.37878v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2609.37878
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Submission history
From: Roke Cepeda-Arroita
[v1] Tue, 29 Sep 2026 15:52:44 UTC (24,362 KB)
https://arxiv.org/abs/2609.37878
Astrobiology, Astrochemistry,
