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