We describe and test a novel Dark Matter Annihilation Feedback (DMAF) scheme that has been implemented into the well known cosmological simulation code GADGET-2. In the models considered here, dark matter can undergo self-annihilation/decay into radiation and baryons. These products deposit energy into the surrounding gas particles and then the dark matter/baryon fluid is self-consistently evolved under gravity and hydrodynamics. We present tests of this new feedback implementation in the case of idealised dark matter halos with gas components for a range of halo masses, concentrations and annihilation rates. For some dark matter models, DMAF's ability to evacuate gas is enhanced in lower mass, concentrated halos where the injected energy is comparable to its gravitational binding energy. Therefore, we expect the strongest signs of dark matter annihilation to imprint themselves onto the baryonic structure of concentrated dwarf galaxies through their baryonic fraction and star formation history. Finally we present preliminary results of the first self-consistent DMAF cosmological box simulations showing that the small scale substructure is washed out for large annihilation rates.

The existence of substructure in halos of annihilating dark matter would be expected to substantially boost the rate at which annihilation occurs. Ultracompact minihalos of dark matter (UCMHs) are one of the more extreme examples of this. The boosted annihilation can inject significant amounts of energy into the gas of a galaxy over its lifetime. Here we determine the impact of the boost factor from UCMH substructure on the heating of galactic gas in a Milky Way-type galaxy, by means of N-body simulation. If 1% of the dark matter exists as UCMHs, the corresponding boost factor can be of order 10 5 . For reasonable values of the relevant parameters (annihilation cross section 3 × 10 −26 cm 3 s −1 , dark matter mass 100 GeV, 10% heating efficiency), we show that the presence of UCMHs at the 0.1% level would inject enough energy to eject significant amounts of gas from the halo, potentially preventing star formation within ∼1 kpc of the halo centre.

We present a new self-consistent method for incorporating dark matter annihilation feedback (DMAF) in cosmological N-body simulations. The power generated by DMAF is evaluated at each dark matter (DM) particle which allows for flexible energy injection into the surrounding gas based on the specific DM annihilation model under consideration. Adaptive, individual time steps for gas and DM particles are supported and a new time-step limiter, derived from the propagation of a Sedov-Taylor blast wave, is introduced. We compare this donor-based approach with a receiver-based approach used in recent studies and illustrate the differences by means of a toy example. Furthermore, we consider an isolated halo and a cosmological simulation and show that for these realistic cases, both methods agree well with each other. The extension of our implementation to scenarios such as non-local energy injection, velocity-dependent annihilation cross-sections, and DM decay is straightforward.

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.

We introduce the concept of directly exciting the lower level of a laser transition in addition to the upper laser level for the provision of new possibilities for light emission from a fiber. In a first demonstration, using diode laser light at 1150 and 1950 nm, we respectively excite the upper and lower laser level of the 5I(6)→5I(7) transition (2.9 μm) of Ho3+-doped ZBLAN, demonstrating a power-scalable arrangement that can switch between free-running and superluminescent spectral output. The spectral composition of the gain-switched pulse derived from modulating the upper laser level pump light depends entirely on the degree of lower laser level excitation at 1950 nm.