  We present a comprehensive series of dissipationless N-body simulations to
investigate the evolution of density distribution in equal-mass mergers between
dark matter (DM) halos and multicomponent galaxies. The DM halo models are
constructed with various asymptotic power-law indices ranging from steep cusps
to core-like profiles and the structural properties of the galaxy models are
motivated by the LCDM paradigm of structure formation. The adopted force
resolution allows robust density profile estimates in the inner ~1% of the
virial radii of the simulated systems. We demonstrate that the central slopes
and overall shapes of the remnant density profiles are virtually identical to
those of the initial systems suggesting that the remnants retain a remarkable
memory of the density structure of their progenitors, despite the relaxation
that accompanies merger activity. We also find that halo concentrations remain
approximately constant through hierarchical merging involving identical systems
and show that remnants contain significant fractions of their bound mass well
beyond their formal virial radii. These conclusions hold for a wide variety of
initial asymptotic density slopes, orbital energies, and encounter
configurations, including sequences of consecutive merger events, simultaneous
mergers of severals ystems, and mergers of halos with embedded cold baryonic
components in the form of disks, spheroids, or both. As an immediate
consequence, the net effect of gas cooling, which contracts and steepens the
inner density profiles of DM halos, should be preserved through a period of
dissipationless major merging. Our results imply that the characteristic
universal shape of DM density profiles may be set early in the evolution of
halos.
