Dark matter mass loss in galaxy flybys: dependence on impact parameter
  Galaxy flybys, interactions where two independent halos inter-penetrate but
detach at a later time and do not merge, occur frequently at lower redshifts.
These interactions can significantly impact the evolution of individual
galaxies - from the mass loss and shape transformation to the emergence of
tidal features and formation of morphological disc structures. The main focus
of this paper is on the dark matter mass loss of the secondary, intruder
galaxy, with the goal of determining a functional relationship between the
impact parameter and dark matter mass loss. Series of N-body simulations of
typical galaxy flybys (10:1 mass ratio) with differing impact parameters show
that the dark matter halo leftover mass of the intruder galaxy follows a
logarithmic growth law with impact parameter, regardless of the way the total
halo mass is estimated. The lost mass then, clearly, follows the exponential
decay law. The stellar component stretches faster as the impact parameter
decreases, following the exponential decay law with impact parameter.
Functional dependence on impact parameter in all cases seems universal, but the
fitting parameters are likely sensitive to the interaction parameters and
initial conditions (e.g. the mass ratio of interacting galaxies, initial
relative velocity of the intruder galaxy, interaction duration). While typical
flybys, investigated here, could not be the sole culprit behind the formation
of ultra-diffuse or dark matter deficient galaxies, they can still contribute
significantly. Rare, atypical and stronger flybys are worth further exploring.
