On the origin of cusps in dark matter halos

Observed cusps with density profiles p proportional to r(-1) or shallower in the central regions of galaxies cannot be reproduced in the standard cold dark matter picture of hierarchical clustering. Previous claims to the contrary were based on simulations with relatively few particles and substantial softening. We present simulations with particle numbers 1 order of magnitude higher and essentially no softening, and we show that typical central density profiles are clearly steeper than p proportional to r(-1). The observed shallower profiles may have formed through the smoothing effect of the spiral-in of central black holes in previous merger phases. In addition, we confirm the presence of a temperature inversion in the inner 5 kpc of massive galactic halos and illustrate its formation as a natural result of the merging of unequal progenitors.