# The GRIFFIN project -- Formation of star clusters with individual massive stars in a simulated dwarf galaxy starburst

**Authors:** Natalia Lahén, Thorsten Naab, Peter H. Johansson, Bruce Elmegreen, Chia-Yu Hu, Stefanie Walch, Ulrich P. Steinwandel, Benjamin P. Moster  
**arXiv:** [1911.05093](https://arxiv.org/abs/1911.05093)  
**Date:** 2019-11-12  
**Summary page:** https://www.summarizepaper.com/en/paper/1911.05093v1/

## Key points

- The GRIFFIN project presents a hydrodynamical simulation of a gas-rich dwarf galaxy merger
- Simulation is resolved with individual massive stars at sub-parsec spatial resolution
- Investigation of star formation environment across various merger phases
- Young star clusters (SCs) described, with masses greater than $M_{\mathrm{*,cl}}\sim 10^{2.5}\,M_{\odot}$ forming along a mass function with a power-law index $\alpha\sim-1.7$ ($\alpha\sim-2$ for $M_{\mathrm{*,cl}}\gtrsim10^{3}\,M_{\odot}$) at all merger phases
- Cluster formation efficiency varies from $\Gamma\sim20\%$ in early merger phases to $\Gamma\sim80\%$ at the peak of the starburst and is compared to observations and model predictions
- Normalization and highest SC masses (up to $\sim 10^6 M_{\odot}$) correlate with the global star formation rate surface density ($\Sigma_\mathrm{SFR}$), which varies by more than three orders of magnitude during the simulation
- Massive SCs ($ \gtrsim 10^4 M_{\odot}$) have sizes and mean surface densities similar to observed young massive SCs, while simulated lower mass clusters appear slightly more concentrated than observed
- All SCs form on timescales of a few Myr and lose their gas rapidly resulting in typical stellar age spreads between $\sigma \sim 0.1 - 2$ Myr ($1 \sigma$), consistent with observations
- Age spreads increase with cluster mass, with the most massive cluster ($ \sim 10^6 M_{ \odot } $) reaching a spread of $5$ Myr once its hierarchical formation finishes
- Study demonstrates the feasibility of investigating the SC population of entire galaxies with high-resolution numerical simulations
- Results provide valuable insights into the formation and evolution of SCs in gas-rich dwarf galaxy mergers, which can be compared to observations and used to refine theoretical models.

## Summary

The GRIFFIN project presents a hydrodynamical simulation of a gas-rich dwarf galaxy merger, resolved with individual massive stars at sub-parsec spatial resolution. The simulation spans seven orders of magnitude in gas surface density and thermal pressure, allowing for the investigation of the star formation environment across various merger phases. The resulting population of young star clusters (SCs) is described, with masses greater than $M_{\mathrm{*,cl}}\sim 10^{2.5}\,M_{\odot}$ forming along a mass function with a power-law index $\alpha\sim-1.7$ ($\alpha\sim-2$ for $M_{\mathrm{*,cl}}\gtrsim10^{3}\,M_{\odot}$) at all merger phases. The cluster formation efficiency varies from $\Gamma\sim20\%$ in early merger phases to $\Gamma\sim80\%$ at the peak of the starburst and is compared to observations and model predictions. The normalization and highest SC masses (up to $\sim 10^6 M_{\odot}$) correlate with the global star formation rate surface density ($\Sigma_\mathrm{SFR}$), which varies by more than three orders of magnitude during the simulation. The massive SCs ($ \gtrsim 10^4 M_{\odot}$) have sizes and mean surface densities similar to observed young massive SCs, while simulated lower mass clusters appear slightly more concentrated than observed. All SCs form on timescales of a few Myr and lose their gas rapidly resulting in typical stellar age spreads between $\sigma \sim 0.1 - 2$ Myr ($1 \sigma$), consistent with observations. The age spreads increase with cluster mass, with the most massive cluster ($ \sim 10^6 M_{ \odot } $) reaching a spread of $5$ Myr once its hierarchical formation finishes. This study demonstrates the feasibility of investigating the SC population of entire galaxies with high-resolution numerical simulations. The results provide valuable insights into the formation and evolution of SCs in gas-rich dwarf galaxy mergers, which can be compared to observations and used to refine theoretical models.