Cores in warm dark matter haloes: a Catch 22 problem

TL;DR

This study uses high-resolution simulations to examine whether warm dark matter can produce the large cores observed in dwarf galaxies, concluding that standard warm dark matter models cannot account for these cores due to fundamental physical constraints.

Contribution

The paper demonstrates through simulations that standard warm dark matter models cannot produce sufficiently large cores in dwarf galaxies, challenging their viability as an explanation for observed galaxy cores.

Findings

Simulated core sizes match theoretical predictions based on Liouville's theorem.

A 0.1 keV warm dark matter particle is needed for a 1 kpc core in dwarf galaxies.

Higher mass warm dark matter candidates produce cores too small to explain observations.

Abstract

The free streaming of warm dark matter particles dampens the fluctuation spectrum, flattens the mass function of haloes and imprints a fine grained phase density limit for dark matter structures. The phase space density limit is expected to imprint a constant density core at the halo center on the contrary to what happens for cold dark matter. We explore these effects using high resolution simulations of structure formation in different warm dark matter scenarios. We find that the size of the core we obtain in simulated haloes is in good agreement with theoretical expectations based on Liouville's theorem. However, our simulations show that in order to create a significant core, (r_c~1 kpc), in a dwarf galaxy (M~1e10 Msun), a thermal candidate with a mass as low as 0.1 keV is required. This would fully prevent the formation of the dwarf galaxy in the first place. For candidates satisfying large scale structure constrains (m_wdm larger than 1-2 keV) the expected size of the core is of the order of 10 (20) pc for a dark matter halo with a mass of 1e10 (1e8) Msun. We conclude that "standard" warm dark matter is not viable solution for explaining the presence of cored density profiles in low mass galaxies.