Re-examining the Too-Big-To-Fail Problem for Dark Matter Haloes with Central Density Cores

TL;DR

This study re-examines the too-big-to-fail problem for dark matter haloes by considering models with shallower central density profiles, finding that the problem diminishes as the density cusp becomes less steep.

Contribution

It demonstrates that the TBTF problem can be alleviated if dark matter haloes have central density slopes shallower than -0.6, challenging previous assumptions of steep cusps.

Findings

Shallower density cusps reduce the TBTF problem.

The TBTF problem is avoided if the central cusp slope is shallower than -0.6.

Central density structure impacts the TBTF problem significantly.

Abstract

Recent studies found the densities of dark matter (DM) subhaloes which surround nearby dwarf spheroidal galaxies (dSphs) to be significantly lower than those of the most massive subhaloes expected around Milky Way sized galaxies in cosmological simulations, the so called "too-big-to-fail" (TBTF) problem. A caveat of previous work has been that dark substructures were assumed to contain steep density cusps in the center of DM haloes even though the central density structure of DM haloes is still under debate. In this study, we re-examine the TBTF problem for models of DM density structure with cores or shallowed cusps. Our analysis demonstrates that the TBTF problem is alleviated as the logarithmic slope of the central cusp becomes shallower. We find that the TBTF problem is avoided if the central cusps of DM haloes surrounding dSphs are shallower than $r^{-0.6}$.