On the persistence of two small-scale problems in {\Lambda}CDM

TL;DR

This study examines whether baryonic physics can resolve two longstanding small-scale issues in the DM model, finding that it does not significantly alter satellite galaxy distributions or resolve the 'too big to fail' problem.

Contribution

The paper provides a comparative analysis showing baryonic physics has limited impact on satellite system structures and challenges recent claims of resolving small-scale DM problems.

Findings

Baryonic physics does not produce more flattened satellite distributions.

Simulations fail to reproduce observed satellite flattening and kinematic coherence.

Adding baryonic physics does not resolve the 'too big to fail' problem.

Abstract

We investigate the degree to which the inclusion of baryonic physics can overcome two long-standing problems of the standard cosmological model on galaxy scales: (i) the problem of satellite planes around Local Group galaxies, and (ii) the "too big to fail" problem. By comparing dissipational and dissipationless simulations, we find no indication that the addition of baryonic physics results in more flattened satellite distributions around Milky-Way-like systems. Recent claims to the contrary are shown to derive in part from a non-standard metric for the degree of flattening, which ignores the satellites' radial positions. If the full 3D positions of the satellite galaxies are considered, none of the simulations we analyse reproduce the observed flattening nor the observed degree of kinematic coherence of the Milky Way satellite system. Our results are consistent with the expectation that baryonic physics should have little or no influence on the structure of satellite systems on scales of hundreds of kiloparsecs. Claims that the "too big to fail" problem can be resolved by the addition of baryonic physics are also shown to be problematic.