First stars contribution to the near-infrared background fluctuations

We show that the emission from the first, metal-free stars inside Population III objects (Pop IIIs) is needed to explain the level of fluctuations in the near-infrared background (NIRB) recently discovered by Kashlinsky et al., at least at the shortest wavelengths. Clustering of (unresolved) Pop IIIs can in fact account for the entire signal at almost all the ∼1–30 arcsec scales probed by observations in the J band. Their contribution fades away at shorter frequencies and becomes negligible in the K band. ‘Normal’, highly clustered, 〈z〉≃ 3 galaxies undergoing intense star formation such as those found in the Hubble Deep Fields can ‘fill in’ this gap and provide for the missing signal. It is in fact found that their contribution to the intensity fluctuations is the dominant one at λ= 2.17 μm, while it gradually loses importance in the H andJ bands. The joint contribution from these two populations of cosmic objects is able, within the errors, to reproduce the observed power spectrum in the whole near-infrared range on small angular scales (θ≲ 200 arcsec for Pop III protogalaxies). Signals on larger scales detected by other experiments instead require the presence of more local sources.