From the last papers:It has become clear that the evolution of matter started earlier than we have known before. For example, Wilkinson Microwave Anisotropy Probe (WMAP) data suggests that reionization began when z ~20 [C.L. Bennet, et al., Astrophys. J. Suppl. 148, 1, (2003)]. According to Refs. [astro-ph/0308005] [M. Dietrich, I. Appenzeller, M. Vestergaard, and S.J. Wagner, Astrophys. J. 564, 581 (2002)], star formation activity started when z >= 10. In addition, it is known that the quasar metallicity did not significantly change from the time of high redshift to the present time [astro-ph/0307557]. Recently a galaxy at z=10.0 was observed [astro-ph/0403025].Other evidences of heavy elements from the high redshifts are in [astro-ph/0309646][astro-ph/0405286][astro-ph/0110123][astro-ph/0201417][astro-ph/0303424] [astro-ph/0305413]
There thus appears to be no evolution of QSO metallicity to z~6. Our results suggest that massive, chemically enriched galaxies formed within 1 Gyr of the Big Bang. If this chemical enrichment was produced by Type Ia supernovae, then the progenitor stars formed at z ~ 20 +/- 10, in agreement with recent estimates based on the cosmic microwave background. These results also support models of an evolutionary link between star formation, the growth of supermassive black holes and nuclear activity.
Is there a problem explaining this early metallicity?This somewhat surprising conclusion may be an indication that the intergalactic medium was enriched in metals at redshifts much greater than 5, perhaps by the sources responsible for its reionization
The standard answer is to say "PopIII stars", but during which epochs and with what mass range? With the constraints on the mass function of such a population can the ubiquitous nature of reionisation and early metallciity be so explained?