Great Balls of FIRE II: The evolution and destruction of star clusters
  across cosmic time in a Milky Way-mass galaxy
  The current generation of galaxy simulations can resolve individual giant
molecular clouds, the progenitors of dense star clusters. But the evolutionary
fate of these young massive clusters (YMCs), and whether they can become the
old globular clusters (GCs) observed in many galaxies, is determined by a
complex interplay of internal dynamical processes and external galactic
effects. We present the first star-by-star $N$-body models of massive
($N\sim10^5-10^7$) star clusters formed in a FIRE-2 MHD simulation of a Milky
Way-mass galaxy, with all of the relevant initial conditions and galactic tidal
effects extracted directly from the cosmological simulation. We randomly select
895 ($\sim 30\%$) of the YMCs with $ > 6\times10^4M_{\odot}$ from Grudi\'c et
al. 2022 and integrate them to the present day using the Cluster Monte Carlo
Code, CMC. This procedure predicts a MW-like system with 148 GCs, most of which
were formed during the early, bursty mode of star formation in the galaxy. Our
GCs are younger, less massive, and more core collapsed than clusters in the
Milky Way or M31. This is a direct result of the assembly history and
age-metallicity relationship of the GCs' host galaxy: younger clusters are
preferentially born in stronger galactic tidal fields and initially retain
fewer stellar-mass black holes, causing them to lose mass faster and reach core
collapse sooner than their older counterparts. Our results suggest that the
masses and core/half-light radii of GCs are shaped not only by internal
dynamical processes, but by the specific evolutionary history of their host
galaxies as well. These results emphasize that $N$-body studies with realistic
stellar physics are crucial to understanding the evolution and present-day
properties of galactic GC systems.
