Is the correlation between the bulge-to-total stellar mass ratio and the number of dwarf galaxies in tension with $\Lambda$CDM?

TL;DR

This study investigates the correlation between galaxy bulge-to-total mass ratio and dwarf satellite count, finding that baryonic physics in simulations aligns with observations and resolves previous tensions with the standard cosmological model.

Contribution

It extends previous analyses with a larger galaxy sample and demonstrates that baryonic effects in simulations produce correlations consistent with observations, challenging prior claims of tension with $ ext{Lambda}$CDM.

Findings

A linear B/T and N$_{250}$ relation in observed galaxies.

Baryonic physics in simulations reproduces the observed correlation.

The empirical relation is consistent with $ ext{Lambda}$CDM}.

Abstract

Previous results suggest that there exists a correlation between the size of the bulge of a galaxy and the number of its dwarf galaxy satellites. This was found to be inconsistent with the standard model of cosmology based on comparisons to semi-analytical dark matter-only simulations, where no such correlation was found. In this work, we extend these studies using the volume-complete ELVES dwarf galaxy catalog, which increases the number of systems compared to previous work by a factor of four. For each giant galaxy we compile the bulge-to-total baryonic mass (B/T) ratio and put it as a function of the number of dwarf galaxies surrounding them within 250 kpc (N$_{250}$). For the 29 galaxy systems in the ELVES catalog, we find a linear relation between B/T and N$_{250}$ which is consistent with previous data. However, for a given stellar mass of the host galaxy this relation is mainly driven by their morphology, where early-type galaxies have a larger B/T ratio and a larger N$_{250}$ than late type galaxies. By investigating spiral galaxies in Illustris-TNG100, we tested whether the inclusion of baryons in the simulations will change the results based on Millennium-II. Contrary to dark matter-only simulations, we do find a correlation between B/T and N$_{250}$, indicating that the standard model of cosmology does predict a correlation. The empirical relation between the number of satellites and the bulge to total stellar mass is therefore not necessarily in tension with $\Lambda$CDM.