The formation of massive stellar clusters in converging galactic flows with photoionization

We have performed simulations of cluster formation along two regions of a spiral arm taken from a global Milky Way simulation, including photoionizing feedback. One region is characterized by strongly converging flows, the other represents a more typical spiral arm region. We find that more massive clusters are able to form on shorter time-scales for the region with strongly converging flows. Mergers between clusters are frequent in the case of the strongly converging flows and enable the formation of massive clusters. We compare equivalent clusters formed in simulations with and without ionization. Photoionization does not prevent massive cluster formation, but can be seen to limit the masses of the clusters. On average, the mass is reduced by around 20 per cent, but we see a large spread from ionization having minimal difference to leading to a 50 per cent reduction in mass. Photoionization is also able to clear out the gas in the vicinity of the clusters on Myr time-scales, which can produce clusters with larger radii that are surrounded by more massive stellar haloes. We find that the ionizing feedback has more impact in our second region that is less dense and has less strongly converging flows.

Automated summary

Our simulations explore the effects of photoionization on cluster formation in different regions of a spiral arm, showing that it has a greater impact in regions with less density and weaker converging flows.