Cuspy no more: how outflows affect the central dark matter and baryon distribution in Λ cold dark matter galaxies

Abstract

We examine the evolution of the inner dark matter (DM) and baryonic density profile of a new sample of simulated field galaxies using fully cosmological, Λ cold dark matter (ΛCDM), high‐resolution SPH+N‐Body simulations. These simulations include explicit H2 and metal cooling, star formation (SF) and supernovae‐driven gas outflows. Starting at high redshift, rapid, repeated gas outflows following bursty SF transfer energy to the DM component and significantly flatten the originally ‘cuspy’ central DM mass profile of galaxies with present‐day stellar masses in the 104.5–109.8 M⊙ range. At z= 0, the central slope of the DM density profile of our galaxies (measured between 0.3 and 0.7 kpc from their centre) is well fitted by ρDM ∝ rα with α≃−0.5 + 0.35 log10(M★/108 M⊙), where M★ is the stellar mass of the galaxy and 4 < log M★ < 9.4. These values imply DM profiles flatter than those obtained in DM‐only simulations and in close agreement with those inferred in galaxies from the THINGS and LITTLE THINGS surveys. Only in very small haloes, where by z= 0 SF has converted less than ∼0.03 per cent of the original baryon abundance into stars, outflows do not flatten the original cuspy DM profile out to radii resolved by our simulations. The mass (DM and baryonic) measured within the inner 500 pc of each simulated galaxy remains nearly constant over 4 orders of magnitudes in stellar mass for M★ < 109 M⊙. This finding is consistent with estimates for faint Local Group dwarfs and field galaxies. These results address one of the outstanding problems faced by the CDM model, namely the strong discrepancy between the original predictions of cuspy DM profiles and the shallower central DM distribution observed in galaxies.

The variation of rotation curve shapes as a signature of the effects of baryons on dark matter density profiles

“…The inner density profile then becomes increasingly flat as stellar mass increases relative to the dark matter mass (Governato et al 2012;, with the greatest flattening when M ∼3×10 8 M . For higher masses, the deeper potential well is able to oppose the halo expansion (Di Cintio et al 2014a,b), resulting in a profile which becomes steeper, and returns to the NFW value at about the Milky Way mass.…”

“…The DC14 profile allows for a range of inner slopes, determined by the stellar-to-halo mass ratio. Galaxies with M ∼ <3×10 6 M are dark matter dominated, and do not produce enough energy to flatten the halo's inner density profile, which remains steep (Peñarrubia et al 2012;Governato et al 2012; Di Cin- Figure 2. 18 rotation curves are shown for the models with NFW and DC14 density profiles in the left and right panels respectively.…”

In-N-Out: The Gas Cycle From Dwarfs to Spiral Galaxies

“…The stellar mass listed in column (7) is calculated directly from the simulation. a Appears in Governato et al (2012). b Appears in Munshi et al (2013).…”

NIHAO IX: the role of gas inflows and outflows in driving the contraction and expansion of cold dark matter haloes

“…On the scale of dwarf galaxies (M200 ∼ 10 10−11 M⊙), a number of different groups have presented fully cosmological hydrodynamical simulations in which the dark matter halo expands (Mashchenko et al 2008;Governato et al 2012;Trujillo-Gomez et al 2015;Chan et al 2015;Tollet et al 2016). In these simulations stellar feedback was found to drive rapid (sub-dynamical) time variability of the potential.…”