Which high-redshift galaxy populations and heating or ionization processes shape the cosmic-dawn 21-cm signal, and can present observations distinguish them?

Scope

In scope

High-redshift galaxies, reionization, X-ray heating, Lyman-alpha coupling, 21-cm power spectra, and cross-correlations.

Out of scope

Early-universe parameter studies without an observable 21-cm or reionization connection.

Why it matters

Turns next-generation 21-cm measurements into identifiable constraints on the first galaxies and heating sources.

Competing explanations

• Low-mass galaxies dominate ionization
• Brighter galaxies with high escape fractions dominate
• X-ray binaries or AGN dominate pre-heating
• Different histories remain non-identifiable in 21-cm statistics

Discriminating observables

• Redshift evolution of the 21-cm power spectrum
• 21-cm cross-correlations with galaxies or the CMB
• JWST luminosity functions and the X-ray background

Blockers

• Foreground removal
• Galaxy-halo mapping
• Escape-fraction and X-ray-efficiency degeneracy
• Sample and simulation coverage