A dark matter profile to model diverse feedback-induced core sizes of ΛCDM haloes

Abstract

We analyze the cold dark matter density profiles of 54 galaxy halos simulated with FIRE-2 galaxy formation physics, each resolved within $0.5\%$ of the halo virial radius. These halos contain galaxies with masses that range from ultra-faint dwarfs (M⋆ ≃ 104.5M⊙) to the largest spirals (M⋆ ≃ 1011M⊙) and have density profiles that are both cored and cuspy. We characterize our results using a new, analytic density profile that extends the standard two-parameter Einasto form to allow for a pronounced constant-density core in the resolved innermost radius. With one additional core-radius parameter, rc, this three-parameter core-Einasto profile is able to characterize our feedback-impacted dark matter halos more accurately than other three-parameter profiles proposed in the literature. In order to enable comparisons with observations, we provide fitting functions for rc and other profile parameters as a function of both M⋆ and M⋆/Mhalo. In agreement with past studies, we find that dark matter core formation is most efficient at the characteristic stellar-mass to halo-mass ratio M⋆/Mhalo ≃ 5 × 10−3, or M⋆ ∼ 109 M⊙, with cores that are roughly the size of the galaxy half-light radius, rc ≃ 1 − 5 kpc. Furthermore, we find no evidence for core formation at radii $\gtrsim 100\ \rm pc$ in galaxies with M⋆/Mhalo < 5 × 10−4 or M⋆ ≲ 106 M⊙. For Milky Way-size galaxies, baryonic contraction often makes halos significantly more concentrated and dense at the stellar half-light radius than DMO runs. However, even at the Milky Way scale, FIRE-2 galaxy formation still produces small dark matter cores of ≃ 0.5 − 2 kpc in size. Recent evidence for a ∼2 kpc core in the Milky Way’s dark matter halo is consistent with this expectation.

Dissipative dark matter on FIRE – I. Structural and kinematic properties of dwarf galaxies

“…Dwarf galaxies have shallower density profiles than the NFW profile. The difference in slope peaks in most massive bright dwarfs where baryonic feedback is most efficient in perturbing galaxy structures, as has been found in previous studies (e.g., Di Cintio et al 2014;Chan et al 2015;Oñorbe et al 2015;Tollet et al 2016;Lazar et al 2020). • In eSIDM, elastic dark matter self-interaction drives the halo to thermal equilibrium and produces an isothermal density profile with a core at the center.…”

“…Details of the measurements of the kinematic properties and relevant definitions are introduced in Section 4.4. Under the influence of baryonic feedback, the density profiles in CDM are generally shallower than the cuspy NFW profiles at galaxy centers, which is expected for these galaxies for their * / halo values (e.g., Di Cintio et al 2014;Chan et al 2015;Oñorbe et al 2015;Tollet et al 2016;Lazar et al 2020). In the eSIDM model, due to effective heat conduction, the profiles are even flatter at galaxy centers compared to the CDM case, but the difference becomes less apparent in the bright dwarf (m11q) where thermal conduction through self-interactions is subdominant compared to baryonic feedback.…”

The central densities of Milky Way-mass galaxies in cold and self-interacting dark matter models

“…Numerical simulations of galaxy formation indicate that feedback-induced core formation is most efficient at * / h ∼ 10 −2 ; galaxies with lower baryon con-version efficiencies retain cuspier profiles, while more complicated effects occur at higher baryon conversion efficiencies. (Di Cintio et al 2014;Chan et al 2015;Tollet et al 2016;Fitts et al 2017;Lazar et al 2020).…”

Deep Search for Decaying Dark Matter with XMM-Newton Blank-Sky Observations

“…[60]). Further, the presence of baryons contracts the inner ∼10 kpc of the profile away from the canonical Navarro, Frenk, and White (NFW) DM distribution [61,62], so that there is an enhancement of the DM density at smaller radii versus the NFW expectation [63][64][65][66][67][68], though cores could develop on top of this contraction at radii ≲2 kpc [69][70][71][72]. For example, in Milky Way analog halos within the Fire-2 simulations the DM-only and hydrodynamic simulations produce DM density profiles that agree within ∼25% at 10 kpc, but with baryons the density profiles are typically around twice as large as the NFW DM-only expectation at distances ∼1 kpc away from the GC [67].…”