The inner structure of haloes in cold+warm dark matter models

Abstract

We analyze the properties of dark matter halos in the cold-plus-warm dark matter cosmologies (CWDM). We study their dependence on the fraction and velocity dispersion of the warm particle, keeping the free-streaming scale fixed. To this end we consider three models with the same free-streaming: (1) a mixture of 90% of CDM and 10% of WDM with the mass 1 keV; (2) a mixture of 50% of CDM and 50% of WDM with the mass 5 keV; and (3) pure WDM with the mass 10 keV. "Warm" particles have rescaled Fermi-Dirac spectrum of primordial velocities (as non-resonantly produced sterile neutrinos would have). We compare the properties of halos among these models and with a ΛCDM with the same cosmological parameters. We demonstrate, that although these models have the same free-streaming length and the suppression of matter spectra are similar at scales probed by the Lyman-α forest (comoving wave-numbers k < 3 − 5 h/Mpc), the resulting properties of halos with masses below ∼ 10 11 M ⊙ are different due to the different behaviour of matter power spectra at smaller scales. In particular, we find that while the number of galaxies remains the same as in ΛCDM case, their density profiles become much less concentrated, and hence in better agreement with current observational constraints. Our results imply that a single parameter (e.g. free streaming length) description of these models is not enough to fully capture their effects on the structure formation process.

Galaxy UV-luminosity function and reionization constraints on axion dark matter

“…The adoption of a lower mass thermally produced DM particle, such as in the WDM scenario, introduces a tension between the desire to produce a core in the inner regions of the DM density profile -favouring a lower mass, while simultaneously producing dwarf galaxies in sufficient number -favouring a higher mass (Macciò et al 2013;Schneider et al 2014). Other effects of WDM, in the case of an ∼ 1keV neutrino, include a significant impact on faint galaxy counts (Schultz et al 2014) and early star formation rates (Dayal, Mesinger & Pacucci 2014).…”

The galactic halo in mixed dark matter cosmologies

“…Recently, a lot of effort has been dedicated to resolve the small-scale structure of CDM haloes [5][6][7], however only a few simulations have been performed to study the WDM scenario [13,38,48], and a single one for the C+WDM model [49]. The aim of this work is to determine the galactic dark matter halo properties in mixed dark matter cosmologies, especially the local dark matter densities of each component.…”

The mass–concentration–redshift relation of cold and warm dark matter haloes

“…The structure of WDM haloes has been studied by Macciò et al (2013) and, more recently, by Bose et al (2016), who report that the NFW formula accounts well for their mass profile shape (see also e.g. Knebe et al 2002;Villaescusa-Navarro & Dalal 2011;Polisensky & Ricotti 2015;González-Samaniego, Avila-Reese & Colín 2016).…”

“…The resulting c(M) relation, however, is non-monotonic: concentrations reach a maximum at a halo mass about two decades above the truncation scale but decline gradually towards larger and smaller masses (see also e.g. Schneider et al 2012;Macciò et al 2013). This implies that fairly massive WDM haloes can be as concentrated as low-mass ones although the shape of their MAHs differ strongly, a feature that is difficult to reconcile with the MAH-based scenario discussed above for CDM.…”