  We investigate whether a single population of first stars could have
influenced both the metal enrichment and reionization of the high-redshift
intergalactic medium (IGM), by calculating the generated ionizing radiation per
unit metal yield as a function of the metallicity of stellar populations. We
examine the relation between the ionizing radiation and carbon created by the
first stars, since the evidence for the widespread enrichment of the IGM at
redshifts $z$ about 3-4 comes from the detection of C IV absorption. We find
that the number of ionizing photons per baryon generated in association with
the detected IGM metallicity may well exceed that required for a late hydrogen
reionization at $z$ of about 6, by up to a factor of 10-20 for metal-free stars
in a present-day initial mass function (IMF). This would be in agreement with
similar indications from recent observations of the microwave background and
the high-$z$ IGM. In addition, the contribution from intermediate-mass stars to
the total metal yield, neglected in past works, substantially impacts such
calculations. Lastly, a top-heavy IMF is not necessarily preferred as a more
efficient high-$z$ source of ionizing radiation, based on nucleosynthetic
arguments in association with a given level of IGM enrichment.
