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Detailed understanding of the formation and evolution of globular clusters (GCs) has been recently advanced through a combination of numerical simulations and analytical models. We employ a state-of-the-art model to create a comprehensive catalogue of simulated clusters in three Milky Way (MW) and three Andromeda (M31) analogue galaxies. Our catalogue aims to connect the chemical and kinematic properties of GCs to the assembly histories of their host galaxies. We apply the model to a selected sample of simulated galaxies that closely match the virial mass, circular velocity profile, and defining assembly events of the MW and M31. The resulting catalogue has been calibrated to successfully reproduce key characteristics of the observed GC systems, including total cluster mass, mass function, metallicity distribution, radial profile, and velocity dispersion. We find that clusters in M31 span a wider range of age and metallicity, relative to the MW, possibly due to M31’s recent major merger. Such a merger also heated up the in-situ GC population to higher orbital energy and introduced a large number of ex-situ clusters at large radii. Understanding the impacts of galaxy mergers and accretion on the GC populations is crucial for uncovering the galaxy assembly histories.

 

The existence of globular clusters (GCs) in a few satellite galaxies, and their absence in majority of dwarf galaxies, present a challenge for models attempting to understand the origins of GCs. In addition to GC presence appearing stochastic and difficult to describe with average trends, in the smallest satellite galaxies GCs contribute a substantial fraction of total stellar mass. We investigate the stochasticity and number of GCs in dwarf galaxies using an updated version of our model that links the formation of GCs to the growth of the host galaxy mass. We find that more than 50 per cent of dwarf galaxies with stellar mass $M_{\star }\lesssim 2\times 10^7\, \mathrm{M}_\odot$ do not host GCs, whereas dwarfs with $M_{\star }\sim 10^8\, \mathrm{M}_\odot$ almost always contain some GCs, with a median number ∼10 at z  = 0. These predictions are in agreement with the observations of the Local Volume dwarfs. We also confirm the near-linear GC system mass–halo mass relation down to $M_{\mathrm{h}}\simeq 10^8\, \mathrm{M}_\odot$ under the assumption that GC formation and evolution in galaxies of all mass can be described by the same physical model. A detailed case study of two model dwarfs that resemble the Fornax dwarf spheroidal galaxy shows that observational samples can be notably biased by incompleteness below detection limit and at large radii.

 

ABSTRACT Globular clusters (GCs) are old massive star clusters that serve as ‘fossils’ of galaxy formation. The advent of Gaia observatory has enabled detailed kinematics studies of the Galactic GCs and revolutionized our understanding of the connections between GC properties and galaxy assembly. However, lack of kinematic measurements of extragalactic GCs limits the sample size of GC systems that we can fully study. In this work, we present a model for GC formation and evolution, which includes positional and kinematic information of individual GCs by assigning them to particles in the Illustris TNG50-1 simulation based on age and location. We calibrate the three adjustable model parameters using observed properties of the Galactic and extragalactic GC systems, including the distributions of position, systemic velocity, velocity dispersion, anisotropy parameter, orbital actions, and metallicities. We also analyse the properties of GCs from different origins. In outer galaxy, ex situ clusters are more dominant than the clusters formed in situ. This leads to the GC metallicities decreasing outwards due to the increasing abundance of accreted, metal-poor clusters. We also find the ex-situ GCs to have greater velocity dispersions and orbital actions, in agreement with their accretion origin. 

ABSTRACT We perform a suite of hydrodynamic simulations to investigate how initial density profiles of giant molecular clouds (GMCs) affect their subsequent evolution. We find that the star formation duration and integrated star formation efficiency of the whole clouds are not sensitive to the choice of different profiles but are mainly controlled by the interplay between gravitational collapse and stellar feedback. Despite this similarity, GMCs with different profiles show dramatically different modes of star formation. For shallower profiles, GMCs first fragment into many self-gravitation cores and form subclusters that distributed throughout the entire clouds. These subclusters are later assembled ‘hierarchically’ to central clusters. In contrast, for steeper profiles, a massive cluster is quickly formed at the centre of the cloud and then gradually grows its mass via gas accretion. Consequently, central clusters that emerged from clouds with shallower profiles are less massive and show less rotation than those with the steeper profiles. This is because (1) a significant fraction of mass and angular momentum in shallower profiles is stored in the orbital motion of the subclusters that are not able to merge into the central clusters, and (2) frequent hierarchical mergers in the shallower profiles lead to further losses of mass and angular momentum via violent relaxation and tidal disruption. Encouragingly, the degree of cluster rotations in steeper profiles is consistent with recent observations of young and intermediate-age clusters. We speculate that rotating globular clusters are likely formed via an ‘accretion’ mode from centrally concentrated clouds in the early Universe.