Bulgeless Evolution And the Rise of Discs (BEARD) III. A numerical simulation view of satellites around Milky-Way analogues

Abstract

$Aims$. The existence of massive disc galaxies with little or no bulge challenges conventional $Λ$ cold dark matter model, which typically favours dynamically hot central structures due to early collapse and mergers. The study of these bulgeless disc galaxies is the aim of the Bulgeless Evolution And the Rise of Discs (BEARD) survey, as they offer a unique opportunity to investigate the link between galaxy morphology and the properties of their satellite systems. $Methods$. Using the high-resolution cosmological hydrodynamical simulation TNG50-1, we studied the satellite populations of 135 bulgeless galaxies. We compared their satellite properties to those of a bulge-dominated control sample with matched stellar masses. Our analysis focuses on satellite abundance, luminosity functions, spatial distribution, orbital alignment, and infall histories. $Results$. We find that satellite abundance is largely independent of host galaxy morphology. However, satellites around bulgeless galaxies exhibit luminosity functions with a steeper faint-end slope, are more centrally concentrated, and show stronger orbital alignment with the host disc plane. The orbital alignment originates from coherent post-infall dynamical evolution that depends on host galaxy morphology. The infall of more massive satellites can additionally perturb this process, contributing to a weakening or temporary stalling of the secular alignment. $Conclusions$. Due to the co-evolution of the host galaxy and the satellite system, the morphology of the central galaxy leaves a clear imprint on its satellite system. Bulgeless galaxies tend to have dynamically colder, more aligned, and more centrally concentrated satellite populations. These trends reflect a more quiet merger history and support the use of satellite properties as tracers of host galaxy formation pathways.