Dark matter annihilation feedback in cosmological simulations – II. The influence on gas and halo structure

Abstract

We present new cosmological hydrodynamic simulations that incorporate Dark Matter Annihilation Feedback (DMAF), whereby energy released from the annihilation of dark matter particles through decay channels such as photon or positron-electron pairs provide additional heating sources for local baryonic material. For annihilation rates comparable to WIMP-like particles, we find that the key influence of DMAF is to inhibit gas accretion onto halos. Such diminished gas accretion early in the lifetimes of halos results in reduced gas fractions in smaller halos, and the delayed halo formation times of larger structures, suggesting that DMAF could impact the stellar age distribution in galaxies, and morphology of dwarfs. For a dark matter particle mass of m χ ∼ 10 MeV, there is a 'critical halo mass' of ∼ 10 13 M at z = 0, below which there are large differences when compared to ΛCDM, such as a reduction in the abundance of halo structures as large as 25 percent, reduced gas content by 50 percent and central gas densities reduced down to 10 percent within halos of mass ∼ 10 12 M but with increasing effects in smaller halos. Higher dark matter particle mass models have a smaller 'critical halo mass'. For a m χ ∼ 100 MeV model, we find differences start appearing below halo masses of ∼ 10 12 M and a m χ 1 GeV model, this mass scale lies below the resolution of our simulations, though we still observe changes in the morphology of dwarf galaxies.

A novel scheme for Dark Matter Annihilation Feedback in cosmological simulations

“…Figure 8 shows a volume rendered representation (see Gárate 2017) of the DM density ρ χ , gas density ρ g , and specific internal energy of the gas u g . It is evident that the strong DMAF in this simulation suppresses the formation of substructure, and the gas density distribution is much more washed out than in the fiducial ΛCDM simulation, as reported in Iwanus et al (2017Iwanus et al ( , 2019.…”

Lux ex tenebris: The imprint of annihilating dark matter on the intergalactic medium during Cosmic Dawn

“…Only for very light DM candidates is the heating strong enough to drive the gas out of haloes, curbing halo formation by a significant amount. Whereas the HMF in Iwanus et al (2019) at high redshift is reduced for a 100 MeV WIMP in a simulation without baryonic cooling physics, this effect is largely erased when taking cooling into account, and the reduction only amounts to ∼ 10% for the smallest haloes. For haloes consisting of N 40 particles, the popular HMF model by Warren et al (2006), which lies between the Press-Schechter and Sheth-Tormen models, matches the reference simulation without DM annihilation well.…”

A black box for dark sector physics: Predicting dark matter annihilation feedback with conditional GANs

“…A self-consistent method for integrating DMAF into cosmological simulations is presented in Iwanus et al (2017). As shown in Iwanus et al (2019) where an in-depth analysis of the results using this method for different dark matter masses is carried out, a major effect of DMAF is to erase small-scale structure in the gas density distribution and to smear the filamentary structure.…”