The central slope of dark matter cores in dwarf galaxies: Simulations vs. THINGS (1011.2777v2)

Abstract: We make a direct comparison of the derived dark matter (DM) distributions between hydrodynamical simulations of dwarf galaxies assuming a LCDM cosmology and the observed dwarf galaxies sample from the THINGS survey in terms of (1) the rotation curve shape and (2) the logarithmic inner density slope alpha of mass density profiles. The simulations, which include the effect of baryonic feedback processes, such as gas cooling, star formation, cosmic UV background heating and most importantly physically motivated gas outflows driven by supernovae (SNe), form bulgeless galaxies with DM cores. We show that the stellar and baryonic mass is similar to that inferred from photometric and kinematic methods for galaxies of similar circular velocity. Analyzing the simulations in exactly the same way as the observational sample allows us to address directly the so-called "cusp/core" problem in the LCDM model. We show that the rotation curves of the simulated dwarf galaxies rise less steeply than CDM rotation curves and are consistent with those of the THINGS dwarf galaxies. The mean value of the logarithmic inner density slopes alpha of the simulated galaxies' dark matter density profiles is ~ -0.4 +- 0.1, which shows good agreement with \alpha = -0.29 +- 0.07 of the THINGS dwarf galaxies. The effect of non-circular motions is not significant enough to affect the results. This confirms that the baryonic feedback processes included in the simulations are efficiently able to make the initial cusps with \alpha ~ -1.0 to -1.5 predicted by dark-matter-only simulations shallower, and induce DM halos with a central mass distribution similar to that observed in nearby dwarf galaxies.