The Infrared Glow of the First Stars

Kashlinsky et al. find a significant cosmic infrared background fluctuation excess on angular scales ≳50 arcsec that cannot be explained by instrumental noise or local foregrounds. The excess has been tentatively attributed to emission from primordial, very massive (Population III, hereafter PopIII) stars formed ≤ 200 Myr after the Big Bang. Using an evolutionary model motivated by independent observations and including various feedback processes, we find that PopIII stars can contribute <40 per cent of the total background intensity (νJν∼ 1–2 nW m−2 sr−1 in the 0.8–8 μm range) produced by all galaxies (hosting both PopIII and PopII stars) at z≥ 5. The infrared fluctuation excess is instead very precisely accounted for by the clustering signal of galaxies at z≥ 5, predominantly hosting PopII stars with masses and properties similar to the present ones.