Formation of Globular Cluster Candidates in Merging Proto-galaxies at
  High Redshift: A View from the FIRE Cosmological Simulations
  Using a state-of-the-art cosmological simulation of merging proto-galaxies at
high redshift from the FIRE project, with explicit treatments of star formation
and stellar feedback in the interstellar medium, we investigate the formation
of star clusters and examine one of the formation hypothesis of present-day
metal-poor globular clusters. We find that frequent mergers in high-redshift
proto-galaxies could provide a fertile environment to produce long-lasting
bound star clusters. The violent merger event disturbs the gravitational
potential and pushes a large gas mass of ~> 1e5-6 Msun collectively to high
density, at which point it rapidly turns into stars before stellar feedback can
stop star formation. The high dynamic range of the reported simulation is
critical in realizing such dense star-forming clouds with a small dynamical
timescale, t_ff <~ 3 Myr, shorter than most stellar feedback timescales. Our
simulation then allows us to trace how clusters could become virialized and
tightly-bound to survive for up to ~420 Myr till the end of the simulation.
Because the cluster's tightly-bound core was formed in one short burst, and the
nearby older stars originally grouped with the cluster tend to be
preferentially removed, at the end of the simulation the cluster has a small
age spread.
