Bin Yue, Andrea Ferrara, Ruben Salvaterra, Xuelei Chen
Several independent measurements have confirmed the existence of a fluctuation excess ($\delta F_{obs}\approx 0.1 nW/m^{2}/sr$ at $3.6 \mu m$) in the Near InfraRed Background (NIRB) up to degree angular scales, whose origin is unknown. By combining high resolution N-body/hydrodynamical cosmological simulations and an analytical model, we predict the absolute intensity and fluctuations impressed on the NIRB by high-$z$ ($z > 5$) galaxies (some of which harboring Pop III stars, shown to provide a negligible contribution) and by simultaneously matching galaxy Luminosity Functions (LFs) and reionization constraints. This strategy also allows us to derive the phenomenological evolution of the ionizing photon escape fraction: we find $f_{esc} = 1$ at $z \ge 11$, decreasing to $\approx 0.05$ at $z = 5$. In the wavelength range $1.0-4.5 \mu m$, the predicted cumulative NIRB flux is $F =0.2-0.04 nW/m^2/sr$. If galaxies brighter than $m_{lim} = 28$ can be removed, the remaining background from stellar sources will still contain a relevant contribution from galaxies at $z > 5$, showing that extraction of the reionization sources signal is feasible. However, we find that the radiation from high-$z$ galaxies (including those undetected by current surveys) is insufficient to explain such excess: at $l=2000$, the fluctuation strength is $\delta F = 0.01-0.002 nW/m^2/sr$, with a relative amplitude $\delta F/F = 4$% almost independent of wavelength. Two problems remain unsolved: (a) both the predicted flux and fluctuations are considerably lower than the observed excess; (b) the fluctuation spectrum is redder ($\lambda_0^p$, with $p = -1.4$) than tentatively measured ($p = -3$). Both facts might indicate that an unknown component/foreground, with a clustering signal very similar to that of high-$z$ galaxies, is dominating the NIRB radiation excess we receive on Earth.
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http://arxiv.org/abs/1208.6234
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