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

Abstract

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 𝜎𝑣 , we also calculate effective J-factors for velocity-dependent models, where the annihilation cross section is either either p-wave (∝ 𝑣 2 /𝑐 2 ) or d-wave (∝ 𝑣 4 /𝑐 4 ). 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.

Sensitivity to sub-GeV dark matter from cosmic-ray scattering with very-high-energy gamma-ray observatories

“…Such a profile is hereafter referred to as the cNFW profile. However, the DM density could still increase JCAP07(2024)012 towards the inner GC as shown in several realizations of the DM distribution of MW-like galaxies from realistic N-body cosmological simulations including baryonic effects [53,54]. We extracted a representative DM distribution from ref.…”

“…We extracted a representative DM distribution from ref. [54], where various hydrodynamical simulations using FIRE-2 zoom-in simulations on MW-like galaxies are performed including radiative heating and cooling of gas, stellar feedback from OB stars, type Ia and type II supernovae, radiation pressure, and star formation effects. A DM profile for representative DM-only FIRE-2 simulation is also extracted.…”