A negligible contribution of two luminous 𝑧 ∼ 7.5 galaxies to the ionizing photon budget of reionization

This repository contains the code, data, and figures used in the publication:

Gazagnes et al. (2025), MNRAS A negligible contribution of two luminous 𝑧 ∼ 7.5 galaxies to the ionizing photon budget of reionization Link to article DOI: https://doi.org/10.1093/mnras/staf768

Summary

In this study, we present JWST/NIRSpec and NIRCam observations of GN 42912, a system of two bright galaxies at 𝑧 ∼ 7.5. We place the first indirect constraints on the escape fraction of ionizing photons (𝑓_esc(LyC)) using the Mg II λλ2796,2803 doublet. Mg II is a promising tracer of LyC leakage, as its ionization potential closely matches that of neutral hydrogen.

Our results provide conservative upper limits on the absolute escape fractions:

• GN 42912-NE: 𝑓_esc(LyC) < 8.5%
• GN 42912-SW: 𝑓_esc(LyC) < 14%

These findings imply a minor contribution of even relatively luminous galaxies to the cosmic reionization photon budget, in tension with bright-galaxy dominated reionization models.

Contents

• Data/ — JWST/NIRSpec and NIRCam reduced data products
• Paper/ — Contains the PDF of the published article
• Notebooks/ — Jupyter notebooks used to generate the paper figures
• Figures/ — Final plots and figures from the publication
• Measurements/ — Emission line fluxes and 𝑓_escmeasurements in CSV format

Highlights

• Mg II-based escape fraction estimates using doublet ratio and photoionization models
• Emission line analysis for [O III], [O II], Hβ, Hγ
• Dust corrections using β slopes with SMC and Reddy attenuation laws
• Comparison with low-redshift LyC emitters and reionization models

Result figures:

This is an overview of the main figures in the paper, which are reproducible with the python notebooks. The paper provides the details and context for the interested reader.

1. Image from photometry:

   

2. Spectrum and line profiles:

   

3. Mg II profile comparison:

4. Escape fraction trends:

   

5. Reionization model comparison:

6. Summary sketch

   

Cite

If you use this repository, please cite:

Gazagnes et al. (2025), Monthly Notices of the Royal Astronomical Society DOI: https://doi.org/10.1093/mnras/staf768