We have investigated cluster formation both in a galactic context and from colliding clouds. We have shown that the density and velocity flows of the gas (dependent on galactic conditions) determine the types of cluster which form. High densities and highly converging flows promote the formation of young massive clusters (Dobbs et al. 2020, Liow et al. 2020). In galaxy scale models, we find that often high density regions also correspond to converging flows, and we find such conditions where there are strong spiral arms. Both Rieder et al. 2022 and Dobbs et al. 2022a highlight that massive clusters in these simulations form by a combination of ongoing star formation, and mergers between smaller clusters.
We modelled the main feedback processes, photoionisation (Bending et al. 2020), supernovae (Bending et al., 2022., Dobbs et al. 2022b, Herrington et al. 2022) and winds (Ali et al. 2022). Photoionisation has the greatest impact on the gas and star formation, and can disperse gas from clusters on Myr timescales (Dobbs et al. 2022). In Dobbs et al. 2022b we show some of the first calculations to produce OB associations (unbound groups of stars). Photoionisation is essential to produce OB associations, and leads to ongoing star formation over several Myr. We produce one association with similar properties (mass, age, size) to Orion. Photoionisation is also required to reproduce the observed cluster radii and masses. We also considered how cluster formation depends on galactic environment by modelling cluster formation in galactic subregions containing a bar, spiral arms and inter-arm regions. We found massive clusters most likely to form in the bar, and inner spiral arms, and OB associations in inter arm and outer arm regions (Ali et al. 2023).
In Dobbs & Wurster 2021, we showed from simulations of colliding flows that the effect of the magnetic field is strongly dependent on its orientation. In later work applying magnetic fields in galactic subregions, where flows are not necessarily continuous, we found that strong magnetic fields can reduce star formation by about 40% (Herrington et al. 2024). We also reproduced the Crutcher relation (magnetic field strength versus density), though we found that for stronger field strengths, the field was too flat with density.
We also produced synthetic observations of the clusters we simulated, including investigating comparing 2D and 3D measurements (Buckner et al. 2022). Whilst we found similar qualitative conclusions with 2D versus 3D, quantitative conclusions including ascertaining cluster substructure, were much less accurate. We also placed our simulated clusters at different distances in the galaxy and calculated their properties using synthetic observations, again finding that identification of substructure within clusters difficult to measure, but also that accurate qualitative observations can be made even with a surprising level of incompleteness (Buckner et al. 2024).
We worked on a method for following individual star particles in larger scale simulations (i.e. at scales above where the stellar initial mass function can be resolved) (Rieder et al. 2022, Liow et al. 2022), in the AMUSE code (and Bending in sphNG). The calculations in Rietder et al. 2022 were able to model stars down to 1 solar mass in a galactic subregion.
