Summary

• Sample: Medium-resolution NIRSpec, 164 MS SF galaxies at z = 2.0 – 9.3 from CEERS survey; bins: z ~ 2.3, z ~ 3.3, z ~ 4.5
• Results:
  • low metallicities and high degrees of ionization are common among early-universe galaxies
  • High-z SF galaxies have harder ionising spectra than typical local galaxies at fixed nebular metallicity
  • Extreme levels of ionization are common among the CEERS/NIRSpec z > 6.5 sample
  • Similarity of the average line ratios → ionisation conditions of ISM do NOT strongly evolve between z ~ 2 - 6 (very different from z = 0 - 2!)
• Remaining questions:
  • Is such high ionization common among all reionization-era galaxies?
  • Are the CEERS z > 6.5 sources representative of the SF population?

Further Reading