Dark matter halo merger histories beyond cold dark matter – I. Methods and application to warm dark matter

Abstract

We describe a methodology to accurately compute halo mass functions, progenitor mass functions, merger rates and merger trees in non-cold dark matter universes using a self-consistent treatment of the generalized extended Press-Schechter formalism. Our approach permits rapid exploration of the subhalo population of galactic halos in dark matter models with a variety of different particle properties or universes with rolling, truncated, or more complicated power spectra. We make detailed comparisons of analytically derived mass functions and merger histories with recent warm dark matter cosmological N-body simulations, and find excellent agreement. We show that, once the accretion of smoothly distributed matter is accounted for, coarse-grained statistics such as the mass accretion history of halos can be almost indistinguishable between cold and warm dark matter cases. However, the halo mass function and progenitor mass functions differ significantly, with the warm dark matter cases being strongly suppressed below the free-streaming scale of the dark matter. We demonstrate the importance of using the correct solution for the excursion set barrier first-crossing distribution in warm dark matter-if the solution for a flat barrier is used instead the truncation of the halo mass function is much slower, leading to an overestimate of the number of low mass halos.

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

“…As may be seen in the figure, the barrier for collapse becomes large for low-mass objects due to the vanishing growth on scales below the Jeans scale. This is consistent with what is found from an excursion-set calculation by Benson et al (2013) applied to WDM at the WDM Jeans scale.…”

The waning of the WIMP? A review of models, searches, and constraints

“…where E is the recoil energy associated to the scattering events, N T is the number of target nuclei per kilogram of the detector, m χ is the DM mass, ρ χ is the local DM density (ρ χ = 0.3 GeV/cm 3 ) [64][65][66][67][68], v is the velocity of the DM particle relative to the Earth, f E (v, t) is the distribution of velocities of the WIMP in the frame of the Earth, 4 v min = m N E/(2μ 2 ) is the minimum WIMP speed required to produce a detectable event at energy E, v esc is the escape velocity i.e., the velocity for which the WIMP are no longer gravitationally bounded to the Milky Way. μ = m χ m N /(m χ + m N ) is the WIMP-nucleus reduced mass (m N is the nucleus mass), dσ /d E(v, E) is the differential cross-section for the WIMP-nucleus scattering as follows,…”

“…As a result, if the DM was produced as a thermal relic in the early Universe, its mass cannot be arbitrarily light. Specifically, cosmological simulations rule out DM masses below a few keV [4][5][6]. (iii) The DM should be electromagnetically neutral, as a result of null searches for stable charged particles [7,8] as well as Direct Detection (DD) experiments, which we will review subsequently.…”

Reionization and Galaxy Formation in Warm Dark Matter Cosmologies

“…The merger-trees use 320 equal redshift steps (Δ z=0.05) between z = 20 and z = 4 with a mass resolution of M res =10 8  M using the modified binary merger tree algorithm with smooth accretion detailed in Parkinson et al (2008) and Benson et al (2013). We scale the relative abundances of the merger tree roots to match the z = 4 Sheth-Tormen HMF (Sheth & Tormen 1999) and have verified that these yield HMFs in good agreement with the Sheth-Tormen HMF at all z.…”