The inner structure of ΛCDM haloes - III. Universality and asymptotic slopes

Abstract

We investigate the mass profile of cold dark matter (ΛCDM) haloes using a suite of numerical simulations spanning five decades in halo mass, from dwarf galaxies to rich galaxy clusters. These haloes typically have a few million particles within the virial radius (r200), allowing robust mass profile estimates down to radii <1 per cent of r200. Our analysis confirms the proposal of Navarro, Frenk & White (NFW) that the shape of the ΛCDM halo mass profiles differs strongly from a power law and depends little on mass. The logarithmic slope of the spherically averaged density profile, as measured by β=−d ln ρ/d ln r, decreases monotonically towards the centre and becomes shallower than isothermal (β < 2) inside a characteristic radius, r−2. The fitting formula proposed by NFW provides a reasonably good approximation to the density and circular velocity profiles of individual haloes; circular velocities typically deviate from NFW best fits by <10 per cent over the radial range that is numerically well resolved. Alternatively, systematic deviations from the NFW best fits are also noticeable. Inside r−2, the profile of simulated haloes becomes shallower with radius more gradually than predicted and, as a result, NFW fits tend to underestimate the dark matter density in these regions. This discrepancy has been interpreted as indicating a steeply divergent cusp with asymptotic inner slope, β0≡β(r = 0) ∼ 1.5. Our results suggest a different interpretation. We use the density and enclosed mass at our innermost resolved radii to place strong constraints on β0: density cusps as steep as r−1.5 are inconsistent with most of our simulations, although β0= 1 is still consistent with our data. Our density profiles show no sign of converging to a well‐defined asymptotic inner power law. We propose a simple formula that reproduces the radial dependence of the slope better than the NFW profile, and so may minimize errors when extrapolating our results inward to radii not yet reliably probed by numerical simulations.

Mixed higgsino dark matter from a large SU(2) gaugino mass

“…We show our results for two halo profiles. The Adiabatically Contracted N03 Halo model [42], where the deepening of the gravitational potential wells caused by baryon in-fall leads to a higher concentration of DM in the center of the the Milky Way, gives higher detection rates, especially for gamma ray and anti-particle detection than smoother halo profiles. For comparison, we also show projections using the Burkert profile [43] where the central cusp in the DM halo is smoothed out by significant heating of cold particles.…”

Halos of unified dark matter scalar field

“…For example for many of the density profiles the slope is n = 3 for large radii [32,33,34,35,36]. In this case a positive energy density ρ > 0 requires n ≥ 2.…”

“…Now, looking at the various CDM density profiles which have been proposed in the literature [31,32,33,34,35,36], we see that we can always take ρ CDM as…”

“…where κ is a proper positive constant which depends on the particular profile that is chosen [31,32,33,34,35,36]. For example for many of the density profiles the slope is n = 3 for large radii [32,33,34,35,36].…”

“…(6) and (8), the expression for the Lagrangian L. Such a procedure establishes a mapping between UDM and CDM solutions that predict the same halo rotation curve v c (r). As a starting point we could, of course, use very different CDM density profiles to this aim, such as the modified isothermal-law profile [31], the Burkert profile [32], the Moore profile [33], the Navarro-Frenk-White profile [34,35] or the profile proposed by Salucci et al (see for example [36]). …”