Empirical Near-Infrared Spectral Templates from SPHEREx: Disentangling AGN and Host-Galaxy Emission
astro-ph.GA, astro-ph.IM
Submitted: 2026-09-02
Updated: 2026-09-02
Comments: 26 pages, 13 figures. Comments are welcome. Codes are available at https://doi.org/10.5281/zenodo.22226283
Code: https://github.com/SPHEREx/Public-products
License: http://creativecommons.org/licenses/by/4.0/
The gist: SPHEREx conducts the first all-sky near-infrared spectral survey over 0.75-5.0 μ m, spanning the transition from host-galaxy starlight to AGN-heated torus emission and enabling spectroscopic
Terminology
Abstract
SPHEREx conducts the first all-sky near-infrared spectral survey over 0.75-5.0 μ m, spanning the transition from host-galaxy starlight to AGN-heated torus emission and enabling spectroscopic identification of active galactic nuclei (AGNs). We develop a data-driven framework combining weighted non-negative matrix factorization with forward modeling to learn empirical rest-frame templates from 2,777 normal galaxies and 1,064 AGNs in the North Ecliptic Pole (NEP) field. The resulting 14-component dictionary contains seven galaxy templates spanning stellar-population continua and nebular emission and seven AGN templates capturing emission lines and warm and hot torus continua, providing an additive, operational decomposition. Inferred near-infrared host fractions correlate with independent SDSS spectral and HSC imaging decompositions (at Pearson r=0.68 and r=0.59), comparable to the SDSS-HSC correlation (r=0.66) and supporting the reliability of the AGN-host separation. In the NEP deep field, the same templates recover redshifts with z fit-z spec < 0.01 for 93.0% of galaxies and 93.5% of AGNs and distinguish galaxies, narrow-line AGNs, and broad-line AGNs with 81.3% accuracy. At all-sky depth, classification retains 72.9% accuracy. The near-infrared coefficients also flag questionable DESI spectral classifications and redshifts, showing how SPHEREx complements optical spectroscopy. Learned directly from survey spectrophotometry and extending beyond the K band, this empirical dictionary fills a long-standing gap in near-to-mid-infrared templates and provides a data-driven foundation for population-scale studies of AGN activity and its connection to host galaxies across the SPHEREx all-sky survey.
Sources
- Three Hundred Quasars from the Couch: A first look at high-redshift quasar discovery with SPHEREx
- DeepDISC-Euclid: Source Classification and Photometric Redshifts in Euclid Deep Field North With a Pixel-Level Deep Learning Approach
- The Dark Energy Spectroscopic Instrument (DESI)
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