Radialization of satellite orbits in galaxy mergers
  We consider the orbital evolution of satellites in galaxy mergers, focusing
on the evolution of eccentricity. Using a large suite of N-body simulations, we
study the phenomenon of satellite orbital radialization -- a profound increase
in the eccentricity of its orbit as it decays under dynamical friction. While
radialization is detected in a variety of different setups, it is most
efficient in the cases of high satellite mass, not very steep host density
profiles, and high initial eccentricity. To understand the origin of this
phenomenon, we run additional simulations with various physical factors
selectively turned off: satellite mass loss, reflex motion and distortion of
the host, etc. We find that all these factors are important for radialization,
since it does not occur for point-mass satellites or when the host potential is
replaced with an unperturbed initial profile. The analysis of forces and
torques acting on both galaxies confirms the major role of self-gravity of both
host and satellite in the reduction of orbital angular momentum. The classical
Chandrasekhar dynamical friction formula, which accounts only for the forces
between the host and the satellite, but not for internal distortions of both
galaxies, does not match the evolution of eccentricity observed in N-body
simulations.
