Diffuse Galactic Backgrounds with SPHEREx: A Pilot Study of Background Modeling and Its Impact on Extinction

We present a spectral analysis of diffuse Galactic background emission using SPHEREx data in a pilot Galactic-plane field, where uncertainty in the estimation of the diffuse infrared background is a major source of systematic uncertainty in extinction studies at near- and mid-infrared wavelengths. We construct channel-resolved background maps across the 0.75–5 μ m range using a large median filter approach and then carry the extinction analysis forward only for the cleaner long-wavelength subset at λ ≥ 3 μ m. In the present field, comparison against an earlier masked-median background model gives a median channel-by-channel background difference of about 6% and a maximum change of ∣Δ τ norm ∣ ≃ 7.4 near 3.205 μ m, underscoring the importance of wavelength-dependent background modeling. These results demonstrate that spectral mapping with SPHEREx provides a practical framework for controlling diffuse background systematics and enables improved constraints on dust opacity and extinction in the Galactic plane.