Understanding Dark Matter Halos part2(Astrophysics + Cosmology)
Concept of Dark Matter Halos
1. Dark matter halo cores and the tidal survival of Milky Way satellites(arXiv)
Author : Raphaël Errani, Julio F. Navarro, Jorge Peñarrubia, Benoit Famaey, Rodrigo Ibata
Abstract : The cuspy central density profiles of cold dark matter (CDM) haloes make them highly resilient to disruption by tides. Self-interactions between dark matter particles, or the cycling of baryons during galaxy formation, may result in the formation of a constant density core which would make haloes more susceptible to tidal disruption. We use N-body simulations to study the evolution of NFW-like “cored” subhaloes in the tidal field of a massive host, and identify the criteria and timescales for full tidal disruption. Applied to the Milky Way (MW), our results imply that the survival of MW satellites places interesting constraints on core formation. Indeed, we find that no subhaloes with cores larger than 1 per cent of their initial NFW scale radius can survive for a Hubble time on orbits with pericentres <10 kpc. A satellite like Tucana 3, with pericentre ~3.5 kpc, must have a core size smaller than ~2 pc to survive just three orbital periods on its current orbit. The core sizes expected in self-interacting dark matter (SIDM) models with a velocity-independent cross section of 1 cm²/g seem incompatible with ultra-faint satellites with small pericentric radii, such as Tuc 3, Seg 1, Seg 2, Wil 1, as these would fully disrupt in less than 10 Gyr after infall. These results suggest that many satellites have vanishingly small core sizes, consistent with CDM cusps. The discovery of further Milky Way satellites on orbits with small pericentric radii would strengthen these conclusions and allow for stricter upper limits on the core sizes implied by the survival of Milky Way satellites.
2.Improved Mixed Dark Matter Halo Model for Ultralight Axions (arXiv)
Author : Sophie M. L. Vogt, David J. E. Marsh, Alex Laguë
Abstract : We present a complete halo model for mixed dark matter composed of cold dark matter (CDM) and ultralight axion-like particles (ULAs). Our model treats ULAs as a biased tracer of CDM, in analogy to treatments of massive neutrinos and neutral hydrogen. The model accounts for clustering of ULAs around CDM host halos, and fully models the cross correlations of both components. The model inputs include the ULA Jeans scale, and soliton density profile. Our model can be used to predict the matter power spectrum, P(k), on non-linear scales for sub-populations of ULAs across the mass range 10−33 eV≤m≤10−21 eV, and can be calibrated against future mixed DM simulations to improve its accuracy. The mixed DM halo model also allows us to assess the importance of various approximations
3.Combined Effects of f(R) Gravity and Massive Neutrinos on the Turn-Around Radii of DarkMatter Halos (arXiv)
Author : Jounghun Lee, Marco Baldi
Abstract : We present a new statistics based on the turn-around radii of cluster halos to break the dark sector degeneracy between the ΛCDM model and the alternative ones with f(R) gravity and massive neutrinos (ν) characterized by the strength of the fifth force, |fR0|, and the total neutrino mass, Mν. Analyzing the rockstar halo catalogs at the present epoch from the {\small DUSTGRAIN}-{pathfinder} N-body simulations performed for four different cosmologies, namely, ΛCDM (|fR0|=0, Mν=0.0eV), fR6 (|fR0|=10−6, Mν=0.0eV), fR6+0.06eV (|fR0|=10−6, Mν=0.06eV) and fR5+0.15eV (|fR0|=10−5, Mν=0.15eV), which are known to yield very similar conventional statistics to one another. For each model, we select those cluster halos which do not neighbor any other larger halos in their bound zones and construct their bound-zone peculiar velocity profiles at z=0. Then, we determine the radial distance of each selected halo at which the bound-zone velocity becomes equal to the recession speed of the Hubble flow as its turn around radius, and evaluate the cumulative probability distribution of the ratios of the turn-around radii to the virial counterparts, P(rt/rv≥α). The degeneracy between the fR6 and fR5+0.15eV models is found to be readily broken by the 10σΔP difference in the value of P(α=4), while the 3.2σΔPdifference between the ΛCDM and fR6+0.06eV models is detected in the value of P(α=8.5). It is also found that the four models yield smaller differences in P(α) at higher redshifts.
