Massive prompt cusps: A new signature of warm dark matter

TL;DR

This paper proposes that prompt density cusps in dark matter halos, especially in warm dark matter models, can serve as observable signatures to distinguish between different dark matter particle masses.

Contribution

It introduces the concept of prompt cusps as a new signature of warm dark matter and explores their potential to constrain WDM particle masses through galaxy kinematics.

Findings

Prompt cusps with masses around 10^7 M_sun are predicted in WDM models.

Prompt cusps can significantly influence the kinematics of Local Group dwarf galaxies.

Constraints on satellite orbits can refine WDM particle mass estimates.

Abstract

Every dark matter halo and subhalo is expected to have a prompt $\rho\propto r^{-1.5}$ central density cusp, which is a relic of its condensation out of the smooth mass distribution of the early universe. The sizes of these prompt cusps are linked to the scales of the peaks in the initial density field from which they formed. In warm dark matter (WDM) models, the smoothing scale set by free streaming of the dark matter can result in prompt cusps with masses of order $10^7$ M$_\odot$. We show that WDM models with particle masses ranging from 2 to 6 keV predict prompt cusps that could detectably alter the observed kinematics of Local Group dwarf galaxies. Thus, prompt cusps present a viable new probe of WDM. A prompt cusp's properties are highly sensitive to when it formed, so prospects can be improved with a better understanding of when the haloes of the Local Group dwarfs originally formed. Tidal stripping can also affect prompt cusps, so constraints on satellite galaxy orbits can further tighten WDM inferences.