Neutralino annihilations and the gas temperature in the dark ages |
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| Authors: | Zacharia Myers Adi Nusser |
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| Institution: | Physics Department, Technion, Haifa 32000, Israel;Asher Space Research Institute, Technion, Haifa 32000, Israel |
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| Abstract: | Assuming that the dark matter is entirely made up of neutralinos, we re-visit the role of their annihilation on the temperature of diffuse gas in the high-redshift universe ( z > 10) , before the formation of luminous structures. We consider neutralinos of particle mass 36 and 100 GeV. The former is able to produce ～7 e ? e + particles per annihilation through the fremionic channel, and the latter ～53 particles assuming a purely bosonic channel. High-energy e ? e + particles up-scatter the cosmic microwave background (CMB) photons into higher energies via the inverse-Compton scattering. The process produces a power-law e ? e + energy spectrum of index ?1 in the energy range of interest, independent of the initial energy distribution. The corresponding energy spectrum of the up-scattered photons is a power law of index ?1/2, if absorption by the gas is not included. The scattered photons photoheat the gas by releasing electrons which deposit a fraction (14 per cent) of their energy as heat into the ambient medium. For uniformly distributed neutralinos, the heating is insignificant. The effect is greatly enhanced by the clumping of neutralinos into dense haloes. We use a time-dependent clumping model which takes into account the damping of density fluctuations on mass-scales smaller than ～10?6 M⊙ . With this clumping model, the heating mechanism boosts the gas temperature above that of the CMB after a redshift of z ～ 30 . By z ≈ 10 , the gas temperature is nearly 100 times its temperature when no heating is invoked. Similar increase is obtained for the two neutralino masses considered. |
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| Keywords: | intergalactic medium cosmology: observations cosmology: theory dark matter large-scale structure of Universe |
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