The gap of stellar mass in galaxy groups: another perspective of the Too-big-To-Fail problem in the Milky Way

TL;DR

This study investigates the 'Too-big-To-Fail' problem in the Milky Way by analyzing satellite galaxy stellar mass gaps, suggesting the Milky Way's formation history naturally avoids the problem without needing modifications to dark matter or baryonic feedback models.

Contribution

It demonstrates that the Milky Way's satellite stellar mass gap can be explained by its unique accretion history, providing a new perspective on the TBTF problem.

Findings

1-2% of galaxy groups show large stellar mass gaps in satellites.

Milky Way likely did not accrete enough massive subhaloes to produce low-velocity satellites.

The stellar mass gap offers an alternative explanation for the TBTF problem.

Abstract

The Milky Way presents the too-big-to-fail (TBTF) problem that there are two observed satellite galaxies with maximum circular velocity larger than 55km/s, and others have velocity less than 25km/s, but the cold dark matter model predicts there should be more than 10 subhaloes with velocity larger than 25km/s. Those massive subhaloes with $25km/s<V_{max}<55km/s$ should not have failed to form stars. The TBTF problem severely challenges the CDM model. Most efforts are seeking the effects of baryonic feedback, decreasing the mass of the Milky Way, changing the properties of dark matter, so as to assign the observed low-velocity satellites into the massive subhaloes found in simulations. However, the TBTF problem can be avoided if the MW have not accreted subhaloes with velocity between $25km/s<V_{max}<55km/s$ although the probability of such a gap is lower as $\sim 1\%$ and can not be tested against observations. In this work we study the gap in stellar mass of satellite galaxies using the SDSS group catalogue and a semi-analytical model. We find that there are 1-2\% of galaxy groups with a large gap in the stellar mass of their satellites. These 'big gap' groups have accreted less massive subhaloes in their formation history and naturally display a gap between their satellite galaxies. If extrapolating our results to the Milky Way is appropriate, we conclude that it is very likely that our Milky Way has not accreted enough massive subhaloes to host those low-velocity satellites, and the TBTF problem is naturally avoided.