2026ApJ...999...29K

Spitzer-based source-subtracted cosmic infrared background (CIB) fluctuations at arcminute-to-degree scales indicate the presence of new populations, whereas subarcminute power arises from known z ≲ 6 galaxies. We reconstruct the evolution of the near-IR CIB anisotropies on subarcminute scales by known galaxy populations. This method is based on, and significantly advanced over, the empirical reconstruction by Helgason et al. which is combined with the halo model connecting galaxies to their host dark matter halos. The modeled CIB fluctuations from known galaxies produce the majority of the observed small-scale signal down to statistical uncertainties of <10% and we constrain the evolution of the halo mass regime hosting such galaxies. Thus, the large-scale CIB fluctuations from new populations are produced by sources with negligible small-scale power. This appears to conflict with the presented intra-halo light models, but is accounted for if the new sources are at high z. Our analysis spanning several Spitzer datasets allows us to narrow the estimated contributions of remaining known galaxies to the CIB anisotropies to be probed potentially from surveys by new and upcoming space missions such as Euclid, SPHEREx, and Roman. Of these, the Roman surveys have the best prospects for measuring the source-subtracted CIB and probing the nature of the underlying new populations at λ < 2 μm, followed by Euclid's surveys, while for SPHEREx the source-subtracted CIB signal from them appears significantly overwhelmed by the CIB from remaining known galaxies.