# The Formation of Star-forming Disks in the TNG50 Simulation

**Authors:** Enci Wang, Simon J. Lilly  
**arXiv:** [2308.02366](https://arxiv.org/abs/2308.02366)  
**Date:** 2023-08-04  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.02366v1/

## Key points

- TNG50 simulation is used to study disk formation
- Analysis of star formation rate surface density, gas inflow and outflow, and angular momentum evolution
- TNG50 galaxies have larger star-forming disks compared to real galaxies in MaNGA survey
- Simulated galaxies show larger deviations from exponential profiles in star formation rate surface density
- Stellar surface density profiles in TNG50 exhibit good exponential profiles due to radial migration of stars
- Radial migration leads to flatter age profiles in TNG50 disks compared to observed galaxies
- Sustained star formation in simulated galaxies driven by net gas inflow
- No evidence for significant loss of angular momentum for accreted gas particles in the simulation
- Adding viscous processes could potentially reduce sizes of simulated disks and produce more realistic profiles
- Acknowledgment of feedback from referee and support from institutions and computing resources

## Summary

In the study, the authors investigate the process of disk formation in the TNG50 simulation by analyzing various aspects such as the profiles of star formation rate surface density ($\Sigma_{\rm SFR}$), gas inflow and outflow, and the evolution of angular momentum of inflowing gas particles. They find that galaxies in the TNG50 simulation tend to have larger star-forming disks compared to real galaxies observed in the MaNGA survey. Additionally, these simulated galaxies show larger deviations from exponential profiles in $\Sigma_{\rm SFR}$. The stellar surface density profiles of TNG50 galaxies, on the other hand, exhibit good exponential profiles due to strong radial migration of stars over time. However, this radial migration leads to flatter age profiles in TNG50 disks compared to observed galaxies. The sustained star formation in simulated galaxies is primarily driven by a net gas inflow, consistent with simple gas-regulator models of galaxies. Interestingly, there is no evidence for significant loss of angular momentum for gas particles after they are accreted onto the galaxy in the simulation. This lack of angular momentum loss may explain the large disk sizes observed in TNG50. However, adding viscous processes such as magnetic stresses from magneto-rotational instability proposed by Wang & Lilly 2022 could potentially reduce the sizes of simulated disks and produce more realistic exponential profiles. The authors acknowledge and appreciate feedback from a referee who helped improve their paper and provided insights into certain aspects of the TNG simulations. They also acknowledge support from various institutions and computing resources used for conducting their research. Overall, this study sheds light on disk formation processes in simulations and highlights potential avenues for future improvements to better match observations.