Fitting functions for dark matter density profiles

We present a unified parametrization of the fitting functions suitable for the density profiles of dark matter haloes or elliptical galaxies. A notable feature is that the classical Einasto profile appears naturally as the continuous limiting case of the cored subfamily amongst the double power-law profiles of Zhao. Based on this, we also argue that there is basically no qualitative difference between halo models fitted well by the Einasto profile and the standard Navarro-Frenk-White model. This might even be the case quantitatively, unless the resolution of simulations and the precision of fittings are sufficiently high to make meaningful distinctions possible.