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Cross-Correlation of Near and Far-Infrared Background Anisotropies as Traced by Spitzer and Herschel

We present the cross-correlation between the far-infrared background fluctuations as measured with the Herschel Space Observatory at 250, 350, and 500 μm and the near-infrared background fluctuations with Spitzer Space Telescope at 3.6 μm. The cross-correlation between far and near-IR background anisotropies are detected such that the correlation coefficient at a few to ten arcminute angular scales decreases from 0.3 to 0.1 when the far-IR wavelength increases from 250 μm to 500 μm. We model the cross-correlation using a halo model with three components: (a) far-IR bright or dusty star-forming galaxies below the masking depth in Herschel maps, (b) near-IR faint galaxies below the masking depth at 3.6 μm, and (c) intra-halo light, or diffuse stars in dark matter halos, that likely dominates fluctuations at 3.6 μm. The model is able to reasonably reproduce the auto correlations at each of the far-IR wavelengths and at 3.6 μm and their corresponding cross-correlations. While the far and near-IR auto-correlations are dominated by faint dusty, star-forming galaxies and intra-halo light, respectively, we find that roughly half of the cross-correlation between near and far-IR backgrounds is due to the same galaxies that remain unmasked at 3.6 μm. The remaining signal in the cross-correlation is due to intra-halo light present in the same dark matter halos as those hosting the same faint and unmasked galaxies. In this model, the decrease in the cross-correlation signal from 250 μm to 500 μm comes from the fact that the galaxies that are primarily contributing to 500 μm fluctuations peak at a higher redshift than those at 250 μm.