Abstract: Tracing the Universe’s Origins

High-redshift cosmology (z≳6), spanning the Cosmic Dawn and the Epoch of Reionization (EoR), currently stands as the central frontier of astrophysics. This review synthesizes recent findings, particularly those enabled by the James Webb Space Telescope (JWST), against the backdrop of the standard ΛCDM cosmological model.

JWST has fundamentally altered the census of the early universe, revealing an unexpected population of massive, evolved galaxies at ultra-high redshifts (z≳10).¹ These structures, appearing mature just ∼300 million years after the Big Bang, introduce a strong tension with CDM’s hierarchical growth predictions, suggesting that either star formation efficiency was radically higher or that fundamental cosmological parameters must be modified (e.g., Early Dark Energy or Constant Creation Cosmology).³ Further conflict exists in 21 cm cosmology, where the highly absorbed signal reported by EDGES at z≈17 points toward an unexpectedly cold baryonic gas, potentially requiring exotic physics such as Scattering Dark Matter (SDM).⁶

Key research themes covered include the confirmed dominance of star-forming galaxies in driving the EoR (6≲z≲10) ⁸, the search for direct and indirect evidence of zero-metallicity Population III stars ⁹, and the growth of Supermassive Black Holes traced by z>6 quasars.¹⁰

We identify critical literature gaps and future imperatives:

1. Observational Gaps: The Cosmic Dark Ages (z≳20) remain unprobed, requiring dedicated radio observatories on the lunar farside.¹¹ Robust spectroscopic confirmation of z≳10 galaxies and accurate constraints on the faint-end slope of the UV luminosity function are crucial for resolving the ionizing photon budget.¹³
2. Theoretical Imperatives: Resolving the ΛCDM tension hinges on meticulously accounting for Cosmic Variance, which dominates the error budget for rare objects at z≳12.¹⁴ Numerical models must transition from approximating the Cosmic Dawn and EoR as separate phases to fully coupled N-body/Radiative Transfer simulations.¹⁵

The path forward demands a strategic, multi-wavelength approach, leveraging the synergistic constraints from JWST, ALMA (for metallicity), the Nancy Grace Roman Space Telescope (for large-scale BAO measurements), and the Square Kilometre Array (SKA) for 21 cm cosmology.¹⁷ The next decade of high-redshift research promises to shift from merely charting cosmic history to definitively testing the fundamental physics governing the universe’s origins.

Tracing the Universe’s Origins: An Exhaustive Review of High-Redshift Cosmology () in the JWST Era

I. Introduction to the High-Redshift Universe: Epochs and Milestones

High-redshift cosmology, conventionally defined as the study of the universe at  (less than a billion years after the Big Bang), represents the frontier of astrophysical investigation. This era is characterized by fundamental phase transitions that set the stage for all subsequent cosmic evolution. Recent observational breakthroughs, particularly from the James Webb Space Telescope (JWST), have necessitated a rigorous re-evaluation of established theoretical models and necessitated a new wave of computational and statistical techniques.

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