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Velocity-dependent J-factors for Milky Way dwarf spheroidal analogues in cosmological simulations

Blanchette, Keagan; Piccirillo, Erin; Bozorgnia, Nassim; Strigari, Louis E.; Fattahi, Azadeh; Frenk, Carlos S.; Navarro, Julio F.; Sawala, Till

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Keagan Blanchette

Erin Piccirillo

Nassim Bozorgnia

Louis E. Strigari

Julio F. Navarro

Till Sawala


We study the impact of the dark matter velocity distribution modelling on signals from velocity-dependent dark matter annihilation in Milky Way dwarf spheroidal galaxies. Using the high resolution APOSTLE simulations, we identify analogues corresponding to Milky Way dwarf spheroidal galaxies, and from these directly determine the dark matter pair-wise relative velocity distribution, and compare to best-fitting Maxwell-Boltzmann distribution models. For three velocity-dependent annihilation models, p-wave, d-wave, and the Sommerfeld model, we quantify the errors introduced when using the Maxwell-Boltzmann parameterization. We extract a simple power-law relation between the maximum circular velocity of the dwarf spheroidal analogue and the peak speed of the Maxwell-Boltzmann distribution. We show that this relation can be used to accurately calculate the dark matter relative velocity distribution, and find that it allows us to estimate the dark matter annihilation signal without the need to directly calculate the relative velocity distribution for each galaxy. The scatter in the J-factors calculated from the analogues dominates the uncertainty obtained when compared to the J-factor as determined from the observational data for each dwarf spheroidal, with the largest scatter from d-wave models and the smallest from Sommerfeld models.


Blanchette, K., Piccirillo, E., Bozorgnia, N., Strigari, L. E., Fattahi, A., Frenk, C. S., …Sawala, T. (2023). Velocity-dependent J-factors for Milky Way dwarf spheroidal analogues in cosmological simulations. Journal of Cosmology and Astroparticle Physics, 2023(03), Article 021.

Journal Article Type Article
Acceptance Date Feb 9, 2023
Online Publication Date Mar 8, 2023
Publication Date 2023-03
Deposit Date May 31, 2023
Publicly Available Date Jun 2, 2023
Journal Journal of Cosmology and Astroparticle Physics
Publisher IOP Publishing
Peer Reviewed Peer Reviewed
Volume 2023
Issue 03
Article Number 021


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Copyright Statement
Published by IOP Publishing Ltd on behalf of Sissa Medialab. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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