We discuss some of the key open questions regarding the formation and evolution of globular clusters (GCs) during galaxy formation and assembly within a cosmological framework. The current state of the art for both observations and simulations is described, and we briefly mention directions for future research. The oldest GCs have ages greater than or equal to 12.5 Gyr and formed around the time of reionization. Resolved colour-magnitude diagrams of Milky Way GCs and direct imaging of lensed proto-GCs at z∼6 with the James Webb Space Telescope (JWST) promise further insight. GCs are known to host multiple populations of stars with variations in their chemical abundances. Recently, such multiple populations have been detected in ∼2 Gyr old compact, massive star clusters. This suggests a common, single pathway for the formation of GCs at high and low redshift. The shape of the initial mass function for GCs remains unknown; however, for massive galaxies a power-law mass function is favoured. Significant progress has been made recently modelling GC formation in the context of galaxy formation, with success in reproducing many of the observed GC-galaxy scaling relations.

We use the spectral synthesis code cloudy to tabulate the properties of gas for an extensive range in redshift (z = 0 - 9), temperature (log T[K] = 1 - 9.5), metallicity (log Z/Z⊙ = −4 - +0.5, Z = 0), and density (log nH[ cm−3] = −8 - +6). This therefore includes gas with properties characteristic of the interstellar, circumgalactic and intergalactic media. The gas is exposed to a redshift-dependent UV/X-ray background, while for the self-shielded lower-temperature gas (i.e. ISM gas) an interstellar radiation field and cosmic rays are added. The radiation field is attenuated by a density- and temperature-dependent column of gas and dust. Motivated by the observed star formation law, this gas column density also determines the intensity of the interstellar radiation field and the cosmic ray density. The ionization balance, molecule fractions, cooling rates, line emissivities, and equilibrium temperatures are calculated self-consistently. We include dust, cosmic rays, and the interstellar radiation field step-by-step to study their relative impact. These publicly available tables are ideal for hydrodynamical simulations. They can be used stand alone or coupled to a non-equilibrium network for a subset of elements. The release includes a C routine to read in and interpolate the tables, as well as an easy to use python graphical user interface to explore the tables.

We present high-resolution simulations of tidal dwarf galaxies (TDG) to investigate their early chemo-dynamical evolution and test their survivability. In this work the simulation setup is introduced and the response of TDGs to self-consistent star formation (SF) and an external tidal field is examined. Throughout the simulation star cluster particles with variable masses down to 5 M ⊙ form, depending on the local gas reservoir. For low cluster masses M cl , the stellar initial mass function (IMF) is considered to be either filled or truncated at a maximal star mass m max to represent the observed m max − M cl relation (IGIMF theory). The evolution of TDGs with fullypopulated and truncated IMFs are compared to study the impact of stellar energy feedback on their survivability. Both TDGs experience an initial starburst but after a dynamical time they evolve into dwarf galaxies with self-regulated and continuous SF. At this stage the truncated-IMF model contains about 6 times more stellar mass than the invariant IMF models, but the final bound gas mass is comparable in both models. In spite of their significantly different SF histories, both TDG models are not disrupted within the first 500 Myr. We conclude that TDGs can survive an early starburst, independent of the underlying IMF description, even though they do not harbor a stabilizing dark matter halo.

In a series of papers, we present detailed chemo-dynamical simulations of tidal dwarf galaxies (TDGs). After the first paper, where we focused on the very early evolution, we present in this work simulations on the long-term evolution of TDGs, ranging from their formation to an age of 3 Gyr. Dark-matter free TDGs may constitute a significant component of the dwarf galaxy (DG) population. But it remains to be demonstrated that TDGs can survive their formation phase given stellar feedback processes, the time-variable tidal field of the post-encounter host galaxy and its dark matter halo and ram-pressure wind from the gaseous halo of the host. For robust results the maximally damaging feedback by a fully populated invariant stellar IMF in each star cluster is assumed, such that fractions of massive stars contribute during phases of low star-formation rates. The model galaxies are studied in terms of their star-formation history, chemical enrichment and rotational curves. All models evolve into a self-regulated long-term equilibrium star-formation phase lasting for the full simulation time, whereby the TDGs become significantly more compact and sustain significantly higher SFRs through compressive tides than the isolated model. None of the models is disrupted despite the unphysical extreme feedback, and none of the rotation curves achieves the high values observed in real TDGs, despite non-virial gas accretion phases.