Abstract
The `core-cusp' problem has long been considered a key small scale challenge
to the standard LCDM paradigm. Halos in dark matter only simulations exhibit
`cuspy' (NFW-like) density profiles, where density continuously increases
towards the centre. However, many observations of galaxies (particularly in the
dwarf regime) indicate that their dark matter density profiles deviate strongly
from this prediction, with much flatter central regions (`cores'). Here, we use
NewHorizon (NH), a hydrodynamical cosmological simulation which adopts the
standard LCDM cosmology, to investigate core formation and the core-cusp
problem, using a statistically significant number of galaxies in a cosmological
volume. In NH, halos that contain galaxies in the upper M* > 10^10.2 MSun) and
lower (M* < 10^8 MSun) ends of the stellar mass distribution contain cusps.
However, halos that contain galaxies with intermediate (10^8 MSun < M* <
10^10.2 MSun) stellar masses are typically cored. These halos typically have DM
masses between 10^10.2 MSun and 10^11.5 MSun. Cores are created via
supernova-driven gas removal from the central regions of halos, which alters
the central gravitational potential, inducing dark matter to migrate to larger
radii. While all massive (M* > 10^9.5 MSun) galaxies undergo a cored-phase, in
some cases cores can be removed and cusps reformed. This happens if a galaxy
undergoes sustained star formation at high redshift, which results in stars
(which, unlike the gas, cannot be removed by baryonic feedback) dominating the
central gravitational potential. After cosmic star formation peaks, the number
of cores and the mass of the halos they are formed in remain constant
throughout the simulation, indicating that cores are being routinely formed
over cosmic time after a threshold halo mass is reached. The existence of cores
is, therefore, not in tension with the standard paradigm.
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