# CEERS: Increasing Scatter along the Star-Forming Main Sequence Indicates Early Galaxies Form in Bursts

**Authors:** Justin W. Cole, Casey Papovich, Steven L. Finkelstein, Micaela B. Bagley, Mark Dickinson, Kartheik G. Iyer, L. Y. Aaron Yung, Laure Ciesla, Ricardo O. Amorin, Pablo Arrabal Haro, Rachana Bhatawdekar, Antonello Calabro, Nikko J. Cleri, Alexander de la Vega, Avishai Dekel, Ryan Endsley, Eric Gawiser, Mauro Giavalisco, Nimish P. Hathi, Michaela Hirschmann  
**arXiv:** [2312.10152](https://arxiv.org/abs/2312.10152)  
**Date:** 2023-12-15  
**Summary page:** https://www.summarizepaper.com/en/paper/2312.10152v1/

## Key points

- CEERS survey presents the SFR-M$_\ast$ relation for galaxies at redshifts $4.5\leq z\leq 12$
- Photometry of galaxies in rest-UV and rest-optical bands from \jwst\ and \hst\ is modeled using flexible SFHs with \bagpipes
- SFRs are averaged over 10~Myr (\sfrten) and 100~Myr (\sfrcen)
- Larger scatter in $\sfrten-M_\ast$ relation compared to $\sfrcen-M_\ast$ relation at redshifts $z\sim 5-9$
- Scatter increases with redshift and increasing stellar mass up to $z\sim 7, suggesting increase in star formation variability
- Ratio $R_\mathrm{SFR}=\log(\sfrten/\sfrcen)$ decreases on average with increasing stellar mass and redshift
- Star formation "duty cycle" of approximately 40% for galaxies with $\log M_\ast/M_\odot\geq 9.3$ at $z\sim5$, declining to about 20% at $z\sim9$
- Longer lulls in star formation at higher redshift and higher stellar mass, transitioning from periods of higher SFR variability at $z\gtrsim~6$ to smoother SFR evolution at $z\lesssim~4.5$
- Insights into the formation and evolution of galaxies in the early universe

## Summary

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The CEERS survey presents the star-formation-rate (SFR)-stellar-mass (M$_\ast$) relation for galaxies at redshifts $4.5\leq z\leq 12$. The photometry of galaxies in the rest-UV and rest-optical bands from \jwst\ and \hst\ is modeled using flexible star-formation histories (SFHs) with the help of \bagpipes. The SFRs are averaged over 10~Myr (\sfrten) and 100~Myr (\sfrcen), effectively tracing nebular emission lines in the rest-optical (on $\sim10$~Myr timescales) and the UV/optical continuum (on $\sim100$ Myr timescales). The slope, normalization, and intrinsic scatter of the SFR-M$_\ast$ relation are measured, accounting for uncertainties and covariances of galaxy SFRs and $M_\ast$. Results show larger scatter in the $\sfrten-M_\ast$ relation compared to the $\sfrcen-M_\ast$ relation at redshifts $z\sim 5-9$, with $\sigma(\log \sfrcen)=0.4$~dex and $\sigma(\log \sfrten)=0.1$~dex respectively. This scatter increases with redshift and increasing stellar mass up to $z\sim 7$, suggesting an increase in star-formation variability for galaxies at higher redshift. A significant trend is observed in the ratio $R_\mathrm{SFR}=\log(\sfrten/\sfrcen)$, which decreases on average with increasing stellar mass and redshift. This indicates a star-formation "duty cycle" of approximately 40% for galaxies with $\log M_\ast/M_\odot\geq 9.3$ at $z\sim5$, declining to about 20% at $z\sim9$. Furthermore, galaxies experience longer lulls in star formation at higher redshift and higher stellar mass, transitioning from periods of higher SFR variability at $z\gtrsim~6$ to smoother SFR evolution at $z\lesssim~4.5$. These findings provide valuable insights into the formation and evolution of galaxies in the early universe.