Luminosity Functions and Star Formation in High-Redshift Galaxies

Over the past decade, measurement and modelling of luminosity functions at redshifts beyond z ≈ 6 have become pivotal to trace the early stages of galaxy build-up and the evolution of cosmic star formation. A luminosity function quantifies the number density of galaxies as a function of their intrinsic brightness, typically in the rest-frame ultraviolet where young, massive stars dominate. At high redshift, these functions are characterised by a faint-end slope sensitive to low-mass systems and a characteristic luminosity indicating the abundance of bright galaxies. Observational campaigns with the Hubble Space Telescope and, more recently, the James Webb Space Telescope have extended measurements of the UV luminosity function to z > 10, revealing a surprisingly slow decline in the number of luminous sources and hints of an evolving faint-end slope. Model fits often adopt a Schechter function or a double power law and inform theoretical frameworks linking dark matter halo assembly to star formation efficiency. These datasets underpin determinations of the cosmic star formation rate density, which peaks near z = 2–3 and declines towards earlier epochs but may remain elevated during cosmic dawn. Reliable photometric and spectroscopic redshifts, careful treatment of nebular emission and dust, and the study of metal-poor primeval systems all contribute to refining our understanding of how the first generations of stars ignited and influenced reionization and subsequent galaxy formation. These efforts inform models of cosmic reionization, the timeline of structure formation, and calibrate simulations used in interpreting deep-field surveys.

Research from Nature Portfolio

Recent studies have provided the first spectroscopic confirmations of galaxies at cosmic dawn and characterised their physical properties. Spectroscopy of four metal-poor systems at z≈10.3–13.2 has unveiled young stellar populations of 10^7–10^8 solar masses with minimal chemical enrichment, enabling constraints on the neutral hydrogen fraction in the intergalactic medium and demonstrating rapid galaxy emergence within 500 million years of the Big Bang. These observations refine estimates of the UV luminosity function at z > 10, validate photometric selection techniques, and support a scenario in which early star formation proceeds efficiently in low-mass haloes, shaping reionization.

Luminosity Functions and Star Formation in High-Redshift Galaxies publication trend

The graph below shows the total number of articles in luminosity functions and star formation in high-redshift galaxies across all publications each year (not limited to Nature Index journals).

Technical terms

Luminosity Function: Statistical distribution of galaxies’ luminosities per unit volume at a given redshift.

Star Formation Rate Density: Amount of stellar mass formed per unit time per unit volume of the Universe.

Redshift (z): Measure of the cosmic expansion indicating how much the wavelength of light has been stretched; correlates with look-back time.

Schechter Function: Mathematical form used to describe the luminosity function with a characteristic luminosity and power-law slope.

Lyman Break: Sharp drop in galaxy spectra shortward of the Lyman-α wavelength caused by absorption in the intergalactic medium.

References

1. Spectroscopic confirmation of four metal-poor galaxies at z = 10.3–13.2. Nature Astronomy (2023).
2. CEERS Key Paper. I. An Early Look into the First 500 Myr of Galaxy Formation with JWST. The Astrophysical Journal Letters (2023).
3. A Comprehensive Study of Galaxies at z ∼ 9–16 Found in the Early JWST Data: Ultraviolet Luminosity Functions and Cosmic Star Formation History at the Pre-reionization Epoch. The Astrophysical Journal Supplement Series (2023).
4. JADES NIRSpec initial data release for the Hubble Ultra Deep Field. Astronomy & Astrophysics (2024).