JWST Observations Reveal the Mystery of Massive Quenched Galaxies in the Early Universe

• The James Webb Space Telescope (JWST) has identified early-universe galaxies that finished star formation much sooner than previously expected.
• Researchers analyzed 120 post-starburst (PSB) galaxies to identify two distinct mechanisms driving this "quenching" process.
• Early, massive galaxies become compact spheroids through violent mergers, while later, less massive galaxies retain disk-like structures through gentler quenching methods.

Mechanisms of Galactic Quenching

• Star formation requires a supply of cold gas; quenching occurs when this gas is removed, depleted, or heated/agitated by galactic activity.
• Major mergers drive gas into galactic centers to trigger rapid, final star formation, followed by AGN feedback that ejects the remaining gas.
• Alternative processes, such as minor mergers or tidal stripping within galaxy clusters, remove gas supply without destroying the galaxy's disk-dominated morphology.

JWST Research Findings

• A study led by Dr. David Maltby at the University of Nottingham used JWST's PRIMER survey to analyze the structural parameters of 120 PSB galaxies between z=0.5 and z=3.
• Massive PSBs at high redshift (z > 1) exhibit significant residual asymmetry, indicating they underwent dramatic, violent transformations masked by smooth stellar distributions.
• Conversely, lower-mass galaxies found later in the "Cosmic Afternoon" maintain their disk-dominated structures, pointing to less disruptive environmental factors.

Implications and Future Work

• The research demonstrates that galactic quenching follows distinct pathways based on mass and cosmic time.
• Future studies aim to incorporate stellar kinematics to refine the timeline and specific physical triggers of these evolutionary transitions.