The challenge of simulating the star cluster population of dwarf galaxies with resolved interstellar medium

Abstract

We present results on the star cluster properties from a series of high resolution smoothed particles hydrodynamics (SPH) simulations of isolated dwarf galaxies as part of the G project. The simulations at sub-parsec spatial resolution and a minimum particle mass of 4 M incorporate non-equilibrium heating, cooling and chemistry processes, and realise individual massive stars. All the simulations follow feedback channels of massive stars that include the interstellar-radiation field, that is variable in space and time, the radiation input by photo-ionisation and supernova explosions. Varying the star formation efficiency per free-fall time in the range 𝜖 ff = 0.2 -50% neither changes the star formation rates nor the outflow rates. While the environmental densities at star formation change significantly with 𝜖 ff , the ambient densities of supernovae are independent of 𝜖 ff indicating a decoupling of the two processes. At low 𝜖 ff , more massive, and increasingly more bound star clusters are formed, which are typically not destroyed. With increasing 𝜖 ff there is a trend for shallower cluster mass functions and the cluster formation efficiency Γ for young bound clusters decreases from 50% to ∼ 1% showing evidence for cluster disruption. However, none of our simulations form low mass (< 10 3 M ) clusters with structural properties in perfect agreement with observations. Traditional star formation models used in galaxy formation simulations based on local free-fall times might therefore not be able to capture low mass star cluster properties without significant fine-tuning.

A panchromatic view of star cluster formation in a simulated dwarf galaxy starburst

“…The analysis of the population of bound clusters revealed a CMF that builds with a power-law slope of the order of −2 already during the first pericentric passage of the galaxies. Further experiments have shown that the CMF slope is only weakly affected by the star formation efficiency (Hislop et al 2021). The population of bound clusters grows in mass and number especially during the most intense star formation period, during which the efficiency of stars forming in bound clusters (cluster formation efficiency, CFE or Γ, Bastian 2008) peaks at 90% of the total star formation.…”

“…The simulations are a part of the G project 1 (Galaxy Real-1 https://wwwmpa.mpa-garching.mpg.de/~naab/griffin-project izations Including Feedback From INdividual massive stars) which addresses some current challenges of galaxy formation (see e.g. Naab & Ostriker 2017, for a review) allowing for the numerical representation of a resolved ISM (see also Steinwandel et al 2020;Hislop et al 2021). In the (Lahén et al 2020a) simulations we have investigated the formation of a distribution of star clusters in the filamentary, hierarchical structures of the starbursting merging disks.…”

Stellar winds and photoionization in a spiral arm

“…Observations and simulations show that cluster mass functions follow a power law (Lahén et al 2020;Hislop et al 2021), possibly with an exponential tail at high masses (Portegies Zwart et al 2010;Li et al 2017). However, for our models, the small number of clusters and the large scatter between mass bins makes the mass function more difficult to calculate for clusters than for clouds.…”

Introducing EMP-Pathfinder: modelling the simultaneous formation and evolution of stellar clusters in their host galaxies

“…The current state-of-the-art numerical simulations of resolved cluster formation in a galactic environment can resolve the cold dense gas leading to their formation (e.g. Li et al 2017;Kim et al 2018;Li et al 2018;Lahén et al 2019Lahén et al , 2020Ma et al 2020a;Hislop et al 2021;Li et al 2021). These simulations offer exciting new prospects on the influence of the galactic environment on the newborn stellar cluster populations (e.g.…”