The Cosmic Near‐Infrared Background: Remnant Light from Early Stars

Abstract

The redshifted ultraviolet light from early stars at z $ 10 contributes to the cosmic near-infrared background. We present detailed calculations of its spectrum with various assumptions about metallicity and the mass spectrum of early stars. We show that if the near-infrared background has a stellar origin, metal-free stars are not the only explanation of the excess near-infrared background; stars with metals (e.g., Z ¼ 1/50 Z ) can produce the same amount of background intensity as the metal-free stars. We quantitatively show that the predicted average intensity at 1-2 m is essentially determined by the efficiency of nuclear burning in stars, which is not very sensitive to metallicity. We predict I / à ' 4 8 nW m À2 sr À1 , where à is the mean star formation rate at z ¼ 7 15 (in units of M yr À1 Mpc À3 ) for stars more massive than 5 M . On the other hand, since we have very little knowledge about the form of the mass spectrum of early stars, the uncertainty in the average intensity due to the mass spectrum could be large. An accurate determination of the near-infrared background allows us to probe the formation history of early stars, which is difficult to constrain by other means. While the star formation rate at z ¼ 7 15 inferred from the current data is significantly higher than the local rate at z < 5, it does not rule out the stellar origin of the cosmic near-infrared background. In addition, we show that a reasonable initial mass function, coupled with this star formation rate, does not overproduce metals in the universe in most cases and may produce as little as less than 1% of the metals observed in the universe today.

First stars and the extragalactic background light: how recentγ-ray observations constrain the early universe

“…As discussed in Fernandez & Komatsu (2006), the continuum luminosity does not depend on the number density of electrons or protons in the nebula, since, in case of a Strömgren sphere, a higher number density would result in a higher recombination rate and consequently a smaller emission region. This approximation is correct as long as the bulk of the emission comes from the nebula around the star in the host halo.…”

“…They burn at higher temperatures than their successors (Tumlinson et al 2003), producing copious amounts of H and He ionizing photons. The nebula absorption and emission can therefore severely alter the SPS spectra (Santos et al 2002;Schaerer 2002;Fernandez & Komatsu 2006).…”

“…1, the EBL can be used as a probe for the properties of the first stars. While several authors discussed a possible signature from the PopIII stars in the NIRBE (Santos et al 2002;Dwek et al 2005a;Madau & Silk 2005;Salvaterra & Ferrara 2006;Fernandez & Komatsu 2006), we want to focus on the recent limit on the EBL density (Aharonian et al 2006;Mazin & Raue 2007) and what constraints on the properties of the PopIII/LM PopII stars can be derived from these limits. Two properties will be mainly investigated: (1) the SFR and (2) the influence of the metallicity.…”

“…Dwek et al (2005a) find that it is likely a foreground artifact from zodiacal light and not of extragalactic origin 5 . A possible PopIII origin of the NIRBE has been investigated by many authors (Santos et al 2002;Dwek et al 2005a;Madau & Silk 2005;Salvaterra & Ferrara 2006;Fernandez & Komatsu 2006). While Dwek et al (2005a) and Madau & Silk (2005) argue that the number of stars required to produce such an excess would overproduce current metallicity levels and would lead to a too high number of baryons in stars, Fernandez & Komatsu (2006, FK06) find that, if accounting for the final stage of the first stars in more detail, a PopIII origin of the NIRBE seems possible.…”

The Very First Stars: Formation and Reionization of the Universe

“…The ongoing Swift gamma-ray burst (GRB) mission provides us with a possible window into massive star formation at the highest redshifts (Lamb & Reichart 2000;Bromm & Loeb 2002. Measurements of the near-IR cosmic background radiation, both in terms of the spectral energy distribution and the angular fluctuations provide additional constraints on the overall energy production due to the first stars (Santos et al 2002;Magliocchetti et al 2003;Dwek et al 2005;Fernandez & Komatsu 2006;Kashlinsky et al 2005). Understanding the formation of the first sources of light is thus of great interest to observational studies conducted both at high redshifts and in our local Galactic neighborhood.…”