A systematic analysis of star cluster disruption by tidal shocks -- I.
  Controlled N-body simulations and a new theoretical model
  Understanding the evolution of stellar clusters in an evolving tidal field is
critical for studying the disruption of stellar clusters in a cosmological
context. We systematically characterise the response of stellar clusters to
tidal shocks using controlled N-body simulations of clusters with various
properties that are subjected to different types of shocks. We find that the
strength of the shock and the density of the cluster within the half-mass
radius are the dominant properties that drive the amount of mass lost by the
cluster, with the shape of the cluster profile being of minor influence. When
the shock is applied as two separate sub-shocks, the amount of mass loss during
the second sub-shock is sensitive to the gap time between them. Clusters that
experience successive sub-shocks separated by less than their crossing time
attain the same masses and sizes at the end of the simulation. However,
clusters subjected to sub-shocks separated by more than a crossing time
experience different evolutionary histories. The amount of mass lost in the
N-body models and its scaling with shock and cluster properties differs from
that predicted by classical tidal disruption theory. We demonstrate that the
discrepancy is alleviated by including a dependence on the escape time-scale of
unbound stars, analogously to mass loss driven by two-body relaxation. With our
new theoretical model for shock-driven mass loss, the predicted relative
amounts of mass loss agree with the results of the N-body simulations to ~0.3
dex across the full suite of simulations.
