# Dust attenuation law in JWST galaxies at z = 7-8

**Authors:** V. Markov, S. Gallerani, A. Pallottini, L. Sommovigo, S. Carniani, A. Ferrara, E. Parlanti, F. Di Mascia  
**arXiv:** [2304.11178](https://arxiv.org/abs/2304.11178)  
**Date:** 2023-04-21  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.11178v1/

## Key points

- Studying galaxies at high redshifts is important for understanding the early universe and its evolution.
- Attenuation curves in galaxies are related to intrinsic galaxy properties such as metallicity, SFR, and stellar age.
- Empirical dust curves measured in the local universe have been used to describe dust attenuation at early epochs due to lack of observational constraints.
- A modified version of the SED fitting code BAGPIPES was developed to address this issue.
- The team used JWST to constrain dust attenuation curves in three star-forming galaxies at z = 7-8.
- Results showed that their attenuation curves differ from local templates, suggesting PAHs' presence in early galaxies.
- Galaxy properties such as stellar mass and SFR inferred from SED fitting are strongly affected by the assumed attenuation curve and star formation history.
- Accounting for potential diversity in dust attenuation laws is important when analyzing galaxy properties at EoR whose dust properties are still poorly understood.
- Applying this method to a larger sample of galaxies observed with JWST can provide important insights into early universe galaxy and dust properties.

## Summary

The study of galaxies at high redshifts is crucial for understanding the early universe and its evolution. Attenuation curves in galaxies, which depend on dust chemical composition, content, and grain size distribution, are related to intrinsic galaxy properties such as metallicity, star formation rate (SFR), and stellar age. However, due to the lack of observational constraints at high redshifts, empirical dust curves measured in the local universe have been employed to describe the dust attenuation at early epochs. To address this issue, a team of researchers led by V. Markov developed a modified version of the spectral energy distribution (SED) fitting code BAGPIPES that includes a detailed dust attenuation curve parametrization. They exploited the high sensitivity and spectral resolution of the James Webb Space Telescope (JWST) to constrain the dust attenuation curves in three star-forming galaxies at z = 7-8. The results showed that their attenuation curves differ from local templates. One out of three galaxies shows a characteristic Milky Way bump typically associated with small carbonaceous dust grains such as polycyclic aromatic hydrocarbons (PAHs). This is one of the first pieces of evidence suggesting PAHs' presence in early galaxies. Furthermore, they found that galaxy properties such as stellar mass and SFR inferred from SED fitting are strongly affected by the assumed attenuation curve. The adopted star formation history also plays a major role in determining these properties. These findings highlight the importance of accounting for potential diversity in dust attenuation laws when analyzing galaxy properties at the epoch of reionization (EoR), whose dust properties are still poorly understood. The application of this method to a larger sample of galaxies observed with JWST can provide important insights into early universe galaxy and dust properties.