A Search for a Dark Matter Annihilation Signal Toward the Canis Major Overdensity with H.E.S.S.

A search for a dark matter (DM) annihilation signal into γ-rays toward the direction of the Canis Major (CMa) overdensity is presented. The nature of CMa is still controversial and one scenario represents it as a dwarf galaxy, making it an interesting candidate for DM annihilation searches. A total of 9.6 hr of high-quality data were collected with the H.E.S.S. array of Imaging Atmospheric Cherenkov Telescopes, and no evidence for a very high energy γ-ray signal is found. Upper limits on the CMa dwarf galaxy mass of the order of 10⁹ M_☉ are derived at the 95% confidence level (CL) assuming neutralino masses in the range 500 GeV–10 TeV and relatively large annihilation cross sections. Constraints on the velocity-weighted annihilation cross section〈σv〉are calculated for specific weakly interacting massive-particle scenarios, using a Navarro–Frenk–White model for the DM halo profile and taking advantage of numerical simulations of hierarchical structure formation. Assuming a total halo mass of 3 × 10⁸ M_☉, 95% CL exclusion limits of the order of 5 × 10⁻²⁴ cm³ s⁻¹ are reached in the 500 GeV–10 TeV DM particle mass interval.