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Velocity-dependent J-factors for annihilation radiation from cosmological simulations

Board, Erin and Bozorgnia, Nassim and Strigari, Louis E. and Grand, Robert J.J. and Fattahi, Azadeh and Frenk, Carlos S. and Marinacci, Federico and Navarro, Julio F. and Oman, Kyle A. (2021) 'Velocity-dependent J-factors for annihilation radiation from cosmological simulations.', Journal of Cosmology and Astroparticle Physics, 2021 (04). 070.


We determine the dark matter pair-wise relative velocity distribution in a set of Milky Way-like halos in the Auriga and APOSTLE simulations. Focusing on the smooth halo component, the relative velocity distribution is well-described by a Maxwell-Boltzmann distribution over nearly all radii in the halo. We explore the implications for velocity-dependent dark matter annihilation, focusing on four models which scale as different powers of the relative velocity: Sommerfeld, s-wave, p-wave, and d-wave models. We show that the J -factors scale as the moments of the relative velocity distribution, and that the halo-to-halo scatter is largest for d-wave, and smallest for Sommerfeld models. The J -factor is strongly correlated with the dark matter density in the halo, and is very weakly correlated with the velocity dispersion. This implies that if the dark matter density in the Milky Way can be robustly determined, one can accurately predict the dark matter annihilation signal, without the need to identify the dark matter velocity distribution in the Galaxy.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Publisher statement:This is an author-created, un-copyedited version of an article published in Journal of Cosmology and Astroparticle Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at
Date accepted:24 March 2021
Date deposited:23 July 2021
Date of first online publication:27 April 2021
Date first made open access:27 April 2022

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