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 between hydrodynamical simulations of dwarf galaxies assuming a ΛCDM 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 α 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 ΛCDM 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 α of the simulated galaxies' dark matter density profiles is ∼−0.4 ± 0.1, which shows good agreement with α=−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 α ∼−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.

NIHAO – IV: core creation and destruction in dark matter density profiles across cosmic time

“…Thanks to the large number of simulated galaxies in the NI-HAO project we can for the first time extend previous observationsimulation comparisons that were based on a limited number of objects (e.g. Oh et al 2011b). …”

Gravitational tides and dwarf spheroidal galaxies

“…The choice of a pseudo-isothermal profile is supported by the observations of low brightness dwarf galaxies (e.g. de Blok et al 2008;Spano et al 2008;Oh et al 2011;Walker & Peñarrubia 2011), although this profile is likely to enhance tidal effects (Kazantzidis et al 2013). …”

Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

“…Some authors have tried to "save cusps" by emphasizing systematic uncertainties like beam-smearing in the H I rotation data and non-circular motions in the higher-resolution optical rotation data; these could create the appearance of a core. Over the past decade, rotation curve data and mass modeling have improved, and cores in the DM halos of dwarf and low-surface-brightness galaxies are consistently favored (e. g., Marchesini et al 2002;de Blok & Bosma 2002;de Blok et al 2008;Weldrake et al 2003;Gentile et al 2004Gentile et al , 2009Spano et al 2008;Oh et al 2008Oh et al , 2011aDonato et al 2009;Plana et al 2010, Chen & McGaugh 2010). de Blok (2010 concludes that almost all dwarf disk galaxies that have been studied have cored halos.…”

“…The most promising mechanism is rapid ejection of most baryons via star-formation feedback (Navarro, Eke, & Frenk 1996;Gnedin & Zhao 2002;Governato et al 2010;Oh et al 2011a;de Souza et al 2011;Madau, Shen, & Governato 2104;De Cintio et al 2014). The idea is especially compelling for tiny dwarfs.…”