THE CENTRAL SLOPE OF DARK MATTER CORES IN DWARF GALAXIES: SIMULATIONS VERSUS THINGS

Abstract

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