The environmental variation of the cosmic formation histories of stars, clusters, and globular clusters in E-MOSAICS

Marta Reina-Campos

Poster -- Galactic scale ISM and star formation

When and how globular clusters form relative to the field star population has been a long standing question. The cosmic star formation rate peaks at z ~ 2 (or ~10 Gyr ago), when the Universe was more efficient at forming stars. By contrast, globular clusters observed in nearby galaxies formed earlier. I will present the formation histories of stars, clusters and globular clusters across a sample of 25 Milky Way-mass galaxies simulated as part of the E-MOSAICS project. We find that globular clusters ([Fe/H]={-2.5,0}) formed between z=0.5-5 (or 5-13 Gyr ago), but are older on average than the field stars across our galaxy sample. Metal-poor globular clusters ([Fe/H]={-2.5,-1}) formed between z=2-5 (or 10-13 Gyr ago), whereas metal-rich clusters ([Fe/H]={-1,0}) are younger, having formed between z=0.5-2.5 (or 5-11 Gyr ago). In addition, we exploit the range of simulations carried out with different cluster formation physics to quantify their influence on these results. Only when accounting for the environmental dependence of the cluster formation efficiency and the initial cluster mass function is the simulated globular cluster population older than the field stars. Without these physics, the globular clusters are found to be younger than the field stars. This implies that simplified models for GCs in a galaxy formation context (e.g. particle tagging) are unable to reproduce the observation that globular clusters are old, and accurate models must account for the environmental dependence of (globular) cluster formation physics.

Background image: Robert Hurt, IPAC