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Amplified J-factors in the Galactic Center for velocity-dependent darkmatter annihilation in FIRE simulations

McKeown, Daniel and Bullock, James S. and Mercado, Francisco J. and Hafen, Zachary and Boylan-Kolchin, Michael and Wetzel, Andrew and Necib, Lina and Hopkins, Philip F. and Yu, Sijie (2021) Amplified J-factors in the Galactic Center for velocity-dependent darkmatter annihilation in FIRE simulations. . (Unpublished)

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We use FIRE-2 zoom cosmological simulations of Milky Way size galaxy halos to calculate astrophysical J-factors for dark matter annihilation and indirect detection studies. In addition to velocity-independent (s-wave) annihilation cross sections σ_v, we also calculate effective J-factors for velocity-dependent models, where the annihilation cross section is either either p-wave (∝v²/c²) or d-wave (∝v⁴/c⁴). We use 12 pairs of simulations, each run with dark-matter-only (DMO) physics and FIRE-2 physics. We observe FIRE runs produce central dark matter velocity dispersions that are systematically larger than in DMO runs by factors of ∼2.5−4. They also have a larger range of central (∼400 pc) dark matter densities than the DMO runs (ρ_(FIRE)/ρ_(DMO) ≃ 0.5−3) owing to the competing effects of baryonic contraction and feedback. At 3 degrees from the Galactic Center, FIRE J-factors are 5−50 (p-wave) and 15−500 (d-wave) times higher than in the DMO runs. The change in s-wave signal at 3 degrees is more modest and can be higher or lower (∼0.3−6), though the shape of the emission profile is flatter (less peaked towards the Galactic Center) and more circular on the sky in FIRE runs. Our results for s-wave are broadly consistent with the range of assumptions in most indirect detection studies. We observe p-wave J-factors that are significantly enhanced compared to most past estimates. We find that thermal models with p-wave annihilation may be within range of detection in the near future.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper ItemGIZMO code
Bullock, James S.0000-0003-4298-5082
Mercado, Francisco J.0000-0002-5908-737X
Hafen, Zachary0000-0001-7326-1736
Boylan-Kolchin, Michael0000-0002-9604-343X
Wetzel, Andrew0000-0003-0603-8942
Necib, Lina0000-0003-2806-1414
Hopkins, Philip F.0000-0003-3729-1684
Yu, Sijie0000-0002-1019-0341
Additional Information:Attribution 4.0 International (CC BY 4.0) We dedicate this paper to the memory of our dear friend and colleague José Antonio Florez Velázquez. We would like to thank Tyler Kelly for helpful suggestions and assistance in the analysis. We thank Kev Abazajian and Louis Strigari for useful discussions. DM, JSB, and FJM were supported by NSF grant AST-1910346. ZH is supported by a Gary A. McCue postdoctoral fellowship at UC Irvine. PH is supported by NSF Research Grants 1911233 & 20009234, NSF CAREER grant 1455342, NASA grants 80NSSC18K0562, HST-AR-15800.001-A. Numerical calculations were run on the Caltech compute cluster “Wheeler,” allocations FTAHopkins/AST20016 supported by the NSF and TACC, and NASA HEC SMD-16-7592. AW received support from: NSF grants CAREER 2045928 and 2107772; NASA ATP grant 80NSSC20K0513; HST grants AR-15809 and GO-15902 from STScI; a Scialog Award from the Heising-Simons Foundation; and a Hellman Fellowship. MBK acknowledges support from NSF CAREER award AST-1752913, NSF grant AST-1910346, NASA grant NNX17AG29G, and HST-AR-15006, HST-AR-15809, HST-GO-15658, HST-GO-15901, HST-GO-15902, HST-AR-16159, and HST-GO-16226 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. DATA AVAILABILITY. The data supporting the plots within this article are available on reasonable request to the corresponding author. A public version of the GIZMO code is available at
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
University of California, IrvineUNSPECIFIED
Heising-Simons FoundationScialog Award
Hellman FellowshipUNSPECIFIED
Subject Keywords:galaxies: disc – glaxies: formation – cosmology: dark natter – cosmology: theory
Record Number:CaltechAUTHORS:20220228-183255347
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113646
Deposited By: George Porter
Deposited On:28 Feb 2022 23:56
Last Modified:28 Feb 2022 23:56

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