A model for dark matter halos

A halo model is presented that possesses a constant phase-space density (Q) core followed by a radial CDM-like power-law decrease in Q. The motivation for the core is the allowance for a possible primordial phase-space density limit such as the Tremaine-Gunn upper bound. The space density profile derived from this model has a constant-density core and falls off rapidly beyond it. The new model is shown to improve the fits to the observations of LSB galaxy rotation curves, naturally provides a model that has been shown to result in a lengthened dynamical friction timescale for the Fornax dwarf spheroidal galaxy, and predicts a flattening of the density profile within the Einstein radius of galaxy clusters. A constant gas entropy floor is predicted whose adiabatic constant provides a lower limit in accord with observed galaxy cluster values. While "observable-sized'' cores are not seen in standard cold dark matter (CDM) simulations, phase-space considerations suggest that they could appear in warm dark matter (WDM) cosmological simulations and in certain hierarchically consistent SuperWIMP scenarios.