A First Look at Galaxy Flyby Interactions. II. Do Flybys matter?
  In the second paper of this series, we present results from cosmological
simulations on the demographics of flyby interactions to gauge their potential
impact on galaxy evolution. In a previous paper, we demonstrated that flybys --
an interaction where two independent halos inter-penetrate but detach at a
later time and do not merge -- occur much more frequently than previously
believed. In particular, we found that the frequency of flybys increases at low
redshift and is comparable to or even greater than the frequency of mergers for
halos $\gtrsim 10^{11} M_\odot/h$. In this paper, we classify flybys according
to their orbits and the level of perturbation exacted on both the halos
involved. We find that the majority of flybys penetrate deeper than $\sim
R_{half}$ of the primary and have an initial relative speed $\sim 1.6\times
V_{vir}$ of the primary. The typical flyby mass-ratio is $\sim 0.1$ at high $z$
for all halos, while at low $z$, massive primary halos undergo flybys with
small secondary halos. We estimate the perturbation from the flyby on both the
primary and the secondary and find that a typical flyby is mostly
non-perturbative for the primary halo. However, since a massive primary
experiences so many flybys at any given time, they are nearly continually a
victim of a perturbative event. In particular, we find flybys that cause $\sim
1\%$ change in the binding energy of a primary halo occurs $\gtrsim 1 $
Gyr$^{-1}$ for halos $> 10^{10} M_\odot/h$ for $z \lesssim 4$. Secondary halos,
on the other hand, are highly perturbed by the typical encounter, experiencing
a change in binding energy of nearly order unity. Our results imply that flybys
can drive a significant part of galaxy transformation at moderate to lower
redshifts ($z \lesssim 4$). We touch on implications for observational surveys,
mass-to-light ratios, and galaxy assembly bias.
