Galactic chemical evolution: The role of the first stars
  The massive First Stars (the first ones to contribute to the chemical
enrichment of the Universe due to their short lifetimes) are long dead, and
even though efforts to directly observe them in high redshift galaxies are
underway, a step forward in this field will have to wait for JWST and ELT. The
only way to currently validate the picture arising from the most modern
hydro-dynamical simulations of the formation of First Stars is to search for
their imprints left on the oldest stars in our Galaxy. Which imprints are we
looking for? In the last years our group has found that many chemical anomalies
observed in very metal-poor halo stars, as well in the oldest bulge globular
cluster, suggest the first stellar generations to have been fast rotators.
After giving a brief overview of the aforementioned results, we highlight the
impact of fast rotating metal-poor massive stars on the chemical enrichment of
heavy-elements such as Sr and Ba. Indeed, in fast rotating massive stars the
s-process production is boosted. We will show, by means of an inhomogeneous
chemical evolution model, based on stochastic approach to the star formation,
that this fact offers a new twist in the interpretation of the abundance
patterns and scatter observed in very metal-poor halo stars.
