Constraining the PopIII IMF with high-z GRBs
  We study the possibility to detect and distinguish signatures of enrichment
from PopIII stars in observations of PopII GRBs (GRBIIs) at high redshift by
using numerical N-body/hydrodynamical simulations including atomic and
molecular cooling, star formation and metal spreading from stellar populations
with different initial mass functions (IMFs), yields and lifetimes. PopIII and
PopII star formation regimes are followed simultaneously and both a top-heavy
and a Salpeter-like IMF for pristine PopIII star formation are adopted. We find
that the fraction of GRBIIs hosted in a medium previously enriched by PopIII
stars (PopIII-dominated) is model independent. Typical abundance ratios, such
as [Si/O] vs [C/O] and [Fe/C] vs [Si/C], can help to disentangle enrichment
from massive and intermediate PopIII stars, while low-mass first stars are
degenerate with regular PopII generations. The properties of galaxies hosting
PopIII-dominated GRBIIs are not very sensitive to the particular assumption on
the mass of the first stars.
