  The redshifted light of the first (Pop III) stars might substantially
contribute to the near infrared background (NIRB). By fitting recent data with
models including up-to-date Pop III stellar spectra, we find that such stars
can indeed account for the whole NIRB residual (i.e. after `normal' galaxy
contribution subtraction) if the high redshift star formation efficiency is f =
10%-50%, depending on the IMF (the top-heaviest requiring lowest efficiency)
and on the unknown galaxy contribution in the L band (our models, however,
suggest it to be negligible). Such epoch of Pop III star formation ends in all
models by z_end ~ 8.8, with a hard limit z_end < 9 set by J band observations.
To prevent an associated IGM over-enrichment with heavy elements compared to
observed levels in the IGM, pair-instability supernovae must be the dominant
heavy element sources. Alternative explanations must break the light-metal
production link by advocating very massive stars (M > 260 M_sun) locking their
nucleosynthetic products in the compact remnant or by postulating an extremely
inhomogeneous metal enrichment of the Ly alpha forest. We discuss these
possibilities in detail along with the uncertainties related to the adopted
zodiacal light model.
