The abundance of core--collapsed subhalos in SIDM: insights from structure formation in $\Lambda$CDM

• Main Authors: Shah, Neev, Adhikari, Susmita
• Format: Journal Article
• Language: English
• Published: 30-08-2023
• Subjects: Physics - Astrophysics of Galaxies; Physics - Cosmology and Nongalactic Astrophysics
• DOI: 10.48550/arxiv.2308.16342

Dark matter halos can enter a phase of gravothermal core--collapse in the
presence of self-interactions. This phase that follows a core--expansion phase
is thought to be subdominant due to the long time-scales involved. However, it
has been shown that the collapse can be accelerated in tidal environments
particularly for halos that are centrally concentrated. Cosmological
simulations in $\Lambda$CDM give us the full distribution of satellite orbits
and halo profiles in the universe. We use properties of the orbits and profiles
of subhalos from simulations to estimate the fraction of the subhalos in
different host halo environments, ranging from the Large Magellanic
cloud(LMC)--like hosts to clusters, that are in the core--collapse phase. We
use fluid simulations of self--interacting dark matter (SIDM) to evolve
subhalos in their hosts including the effect of tidal truncation at the time of
their pericenter crossing. We find that for parameters that allow the
interaction cross-section to be high at dwarf scales, at least $10~\%$ of all
subhalos are expected to have intrinsically collapsed within Hubble time up to
the group mass host scales. This fraction increases significantly, becoming at
least 20$\%$ when tidal interactions are considered. To identify these objects
we find that we either need to measure their densities at very small radial
scales, where the subhalos show a bimodal distribution of densities, or
alternatively we need to measure the slopes of their inner density profiles
near the scale radius, which are much steeper than NFW slopes expected in cold
dark matter halos. Current measurements of central slopes of classical dwarfs
do not show a preference for collapsed objects, however this is consistent with
an SIDM scenario where the classical dwarfs are expected to be in a cored
phase.