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We use FIRE-2 zoom cosmological simulations of Milky Way size galaxy halos tocalculate astrophysical J-factors for dark matter annihilation and indirectdetection studies. In addition to velocity-independent (s-wave) annihilationcross sections $\sigma_v$, we also calculate effective J-factors forvelocity-dependent models, where the annihilation cross section is eithereither p-wave ($\propto v^2/c^2$) or d-wave ($\propto v^4/c^4$). We use 12pairs of simulations, each run with dark-matter-only (DMO) physics and FIRE-2physics. We observe FIRE runs produce central dark matter velocity dispersionsthat are systematically larger than in DMO runs by factors of $\sim 2.5-4$.They also have a larger range of central ($\sim 400$ pc) dark matter densitiesthan the DMO runs ($\rho_{\rm FIRE}/\rho_{\rm DMO} \simeq 0.5 - 3$) owing tothe competing effects of baryonic contraction and feedback. At 3 degrees fromthe 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 ismore modest and can be higher or lower ($\sim 0.3-6$), though the shape of theemission profile is flatter (less peaked towards the Galactic Center) and morecircular on the sky in FIRE runs. Our results for s-wave are broadly consistentwith the range of assumptions in most indirect detection studies. We observep-wave J-factors that are significantly enhanced compared to most pastestimates. We find that thermal models with p-wave annihilation may be withinrange of detection in the near future.

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