Dark Matter Annihilation in the Milky Way Galaxy: Effects of Baryonic Compression

If the dark matter (DM), which is considered to constitute most of the mass of galaxies, is made of supersymmetric particles, the central region of our Galaxy should emit $\gamma$ rays produced by their annihilation. We use detailed models of the Milky Way to make accurate estimates of continuum $\gamma$-ray fluxes. We argue that the most important effect, which was previously neglected, is the compression of the dark matter due to the infall of baryons to the galactic center: it boosts the expected signal by a factor 1000. To illustrate this effect, we computed the expected $\gamma$ fluxes in the minimal supergravity scenario. Our models predict that the signal could be detected at high confidence levels by imaging atmospheric Čerenkov telescopes assuming that neutralinos make up most of the DM in the Universe.

Figure 1

Left: the top curve is the density of baryons. The dashed and full curves “DM” are for the compressed Moore et al. and NFW models. The long-dashed curve is the uncompressed NFW profile. Right: The solid and dashed curves are the total mass in compressed NFW and Moore et al. models. DM mass in the NFW model is the thick curve. Symbols show observational constraints as taken from Klypin et al. [23].

Figure 2

Allowed WMAP ${\tilde{\chi }}_1^0$ annihilation $⟨\sigma v⟩$ and $f_{\mathrm{S}\mathrm{U}\mathrm{S}\mathrm{Y}}$ in the scanned MSUGRA scenario.

Figure 3

Predicted continuum $\gamma$ fluxes as a function of distance ${\Psi }_0$ from the galactic center. The dashed line give the minimum detectable gamma flux $F_{\min }$ (see text).