# Dead or Alive? How Bursty Star Formation and Patchy Dust Can Cause Temporary Quiescence in High Redshift Galaxies

**Authors:** A. L. Faisst, T. Morishita  
**arXiv:** [2402.13316](https://arxiv.org/abs/2402.13316)  
**Date:** 2024-02-20  
**Summary page:** https://www.summarizepaper.com/en/paper/2402.13316v1/

## Key points

- A galaxy named JADES-GS-z7-01-QU discovered at z=7.3 poses intriguing questions due to its unique characteristics
- Exhibits undetected optical emission lines and a blue UV to optical continuum ratio challenging current theoretical models
- Not classified as "quiescent" based on common color diagrams, experiencing temporary deficit in star formation activity
- Two potential explanations explored: stochastic variations in star formation history (SFH) and spatially varying dust attenuation
- Stochastic star formation model with rapid fluctuations in star formation rates can replicate observed properties
- Composite spectrum comprising blue and red components can reproduce a spectrum featuring a blue UV continuum and absence of emission lines
- Future observations using ALMA expected to provide further insights into scenario involving spatially varying dust attenuation
- Highlights the complexity of early Universe galaxies, emphasizing the need for continued exploration and refinement of theoretical models

## Summary

A recent study has discovered a galaxy at z=7.3, named JADES-GS-z7-01-QU, that poses intriguing questions due to its unique characteristics. This galaxy exhibits undetected optical emission lines and a blue UV to optical continuum ratio that current theoretical models struggle to explain. While not typically classified as "quiescent" based on common color diagrams, this galaxy appears to be experiencing a temporary deficit in star formation activity. To understand the unusual properties of JADES-GS-z7-01-QU, two potential explanations were explored: stochastic variations in star formation history (SFH) and spatially varying dust attenuation affecting the measured line and continuum emission properties. It was found that both scenarios could work together to amplify the observed effects. A stochastic star formation model, resembling realistic SFHs from hydrodynamical simulations of similar-mass galaxies, could replicate the observed properties if star formation rates fluctuate rapidly with a correlation time of less than 200 million years and a burst amplitude of approximately 0.6 dex. The total duration of such an active state is estimated to be less than 20 million years, with a likelihood of occurrence over 500 million years at z=7 being around 50%. Additionally, it was demonstrated that a spectrum featuring a blue UV continuum and absence of emission lines could be reproduced by a composite spectrum comprising both blue and red components. The blue component represents dust-free density bounded HII regions emitting the UV continuum while the red component signifies a dust-obscured starburst with weakened emission lines due to significant differential dust attenuation between stellar and nebular emissions. Future observations using ALMA for resolving far-infrared emissions are expected to provide further insights into the latter scenario involving spatially varying dust attenuation. Overall, the perplexing nature of JADES-GS-z7-01-QU highlights the complexity of early Universe galaxies and underscores the need for continued exploration and refinement of theoretical models to fully understand their evolution.