Heating of galactic gas by dark matter annihilation in ultracompact minihalos

Abstract

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.

3D simulations with boosted primordial power spectra and ultracompact minihalos

“…It is in any case interesting to ask how the dark matter substructure would change if the initial small scale perturbations were larger than expected. Other papers which constrain the power spectrum on small scales include [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. In particular, we note that CMB spectral distortion constraints provide an upper bound on the primordial power spectrum on about the same scales as UCMHs, which are about an order of magnitude weaker than the currently claimed constraints but independent of the DM model [20].…”

Dark matter substructure cannot explain properties of the Fermi Galactic Centre excess

“…This is not an effect of favouring any particular value of M h , as the UCMH substructure boost factor is in fact independent of their mass function[32]. Indeed, in all scans performed here (NFW and UCMH alike) we find equal preference for all values of log 10 (M h /M ) ∈ [−12,9].…”

Point sources from dissipative dark matter

“…UCMHs that form from large fluctuations in the power spectrum have also been considered as potential dark point sources [24][25][26][27][28][29][30][31][32][33]. For the UCMH, in addition to annihilation of dark matter within the UCMH, there will be annihilations of dark matter in the UCMH and in halo, leading to a different radial dependence of the excess.…”