Real and counterfeit cores: how feedback expands haloes and disrupts tracers of inner gravitational potential in dwarf galaxies

The tension between the diverging density profiles in Lambda cold dark matter simulations and the constant-density inner regions of observed galaxies is a long-standing challenge known as the 'core-cusp' problem. We demonstrate that the SMUGGLE galaxy formation model implemented in the arepo moving mesh code forms constant-density cores in idealized dwarf galaxies of M-star approximate to 8 x 10(7) M-sun with initially cuspy dark matter (DM) haloes of M-200 approximate to 10(10) M-sun. Identical initial conditions run with an effective equation of state interstellar medium model preserve cuspiness. Literature on the subject has pointed to the low density threshold for star formation, rho(th), in such effective models as an obstacle to baryon-induced core formation. Using a SMUGGLE run with equal rho(th), we demonstrate that core formation can proceed at low density thresholds, indicating that rho(th) is insufficient on its own to determine whether a galaxy develops a core. We reaffirm that the ability to resolve a multiphase interstellar medium at sufficiently high densities is a more reliable indicator of core formation than any individual model parameter. In SMUGGLE, core formation is accompanied by large degrees of non-circular motion, with gas rotational velocity profiles that consistently fall below the circular velocity out to similar to 2 kpc. Asymmetric drift corrections help recover the average underlying DM potential for some of our less efficient feedback runs, but time-variations in the instantaneous azimuthal gas velocity component are substantial, highlighting the need for careful modelling in the inner regions of dwarfs to infer the true distribution of DM.

Automated summary

The tension between the density profiles in simulated and observed galaxies has long been a challenge. However, the SMUGGLE galaxy formation model implemented in the arepo code is able to form constant-density cores in dwarf galaxies. It is found that the ability to resolve a multiphase interstellar medium at high densities is a more reliable indicator of core formation than any individual model parameter. The presence of non-circular motion and the need for careful modeling in the inner regions of dwarfs highlight the complexity of inferring the true distribution of dark matter.