Baryonic Pinching of Galactic Dark Matter Haloes

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  • 29 August 2006
Abstract
High resolution cosmological N-body simulations of four galaxy scale dark matter haloes are compared to corresponding N-body/hydrodynamical simulations containing DM, stars and gas. The simulations without baryons share features with others described in the literature, in that the DM density slope continuously decreases towards the center, with a density \rho~r^{-1.3+/-0.2} at about 1% of the virial radius. The central cusps, in the simulations which also contain baryons, steepen significantly, to \rho~r^{-1.9+/-0.2}, with an indication of the inner logarithmic slope converging. Models of "adiabatic" contraction of DM haloes, due to the central build-up of stellar/gaseous galaxies, are examined. The simplest model, by Blumenthal et al., is shown to overestimate the central DM density considerably for our two Milky Way sized galaxies. The modified model, proposed by Gnedin et al., is tested, and it is shown, that while it is a considerable improvement for the two galaxies it is not perfect. Implications for DM annihilation at the Galactic center are discussed, and it is found, that although our simulations show a considerable reduced DM halo contraction, as compared to the Blumenthal et al. model, the flux from DM annihilation seem to be enhanced by at least a factor 100 as compared to DM only haloes. Finally, it is shown that while DM only haloes are typically prolate, the DM haloes containing baryons are mildly oblate with minor-to-major axis ratios of c/a=0.73+/-0.11, and with their flattening aligned with the central baryonic disks. Moreover, the central disks appear aligned with the flattest parts of the prolate DM only haloes.

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