Formation and Evolution of Globular Cluster Systems: What have we learned and what's next?

  Thomas H. Puzia 
  Herzberg Institute of Astrophysics

Globular Clusters are the best approximations to simple stellar
populations known to exist. Compared to the complex stellar population
mix of the diffuse (i.e. unresolved) light of their host galaxies,
they offer the only way at present of measuring (spectroscopically)
the *discrete* abundance distribution functions and star formation
histories of stellar populations in galaxies beyond the Local
Group. Given that globular clusters exist in virtually every galaxy
and form during major star-formation episodes they can be used as
tracer populations of star formation and assembly histories of their
host systems. In my talk, I will present recent advance in modeling
the chemical distributions functions of globular cluster systems in
massive elliptical galaxies that appear to require an early and rapid
spherical collapse and subsequent dissipationless hierarchical mass
assembly. The comparison of model predictions with spectroscopic
observations reveals, for the first time, the presence of at least two
distinct enrichment epochs of ancient globular cluster
sub-populations. The chemical signatures of some of these clusters
imply formation epochs which predate those of the vast majority of
stars in massive elliptical galaxies and make them candidates for some
of the first stellar generations in the Universe. I will briefly
discuss these exciting results in the context of hierarchical galaxy
formation. Illustrating the next-generation of stellar evolution
computations and population synthesis models, I will explain new
diagnostic tools and some of the multi-faceted follow-up observational
tests that can be performed using current and future facilities that
will greatly advance our understanding of the very early galaxy
formation processes.