Evolutionary Dynamics of Massive Galaxies

The evolution of the most massive galaxies unfolds through a complex interplay of internal processes and external interactions. In the early Universe, rapid in situ star formation and gas-rich mergers drive the assembly of compact stellar cores. As cosmic time advances, these systems experience quenching of star formation—often linked to feedback from active galactic nuclei—and transition into quiescent phases. Subsequent growth is dominated by the accretion of lower-mass satellites via minor mergers, which progressively build extended stellar envelopes in an inside-out fashion. Meanwhile, major mergers can reshape morphologies, transforming disky progenitors into spheroid-dominated remnants and altering kinematic profiles. Observations at optical, infrared and sub-millimetre wavelengths, together with cosmological hydrodynamical simulations, reveal a mass-dependent growth pattern: the most massive galaxies form their central cores earliest and subsequently increase in size and mass more gradually. Environmental factors further modulate evolutionary pathways, with dense regions supporting accelerated merging and assembly. The net result is a population of present-day massive ellipticals whose stellar populations carry imprints of early, dissipative formation and later, primarily dissipationless growth. Understanding these dynamics not only constrains models of baryonic and dark matter assembly but also informs interpretations of galaxy scaling relations and the cosmic history of star formation.

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Evolutionary Dynamics of Massive Galaxies publication trend

The graph below shows the total number of articles in evolutionary dynamics of massive galaxies across all publications each year (not limited to Nature Index journals).

Technical terms

Minor merger: The accretion of a much less massive galaxy (mass ratio typically below 1:4) onto a more massive host, contributing to size and mass growth without dramatically disrupting the host’s structure.

Quiescent galaxy: A galaxy with little or no ongoing star formation, characterised by red colours and dominated by older stellar populations.

Half-light radius: The radius within which half of a galaxy’s total light (or stellar mass in a given band) is contained, often used as a proxy for galaxy size.

Redshift (z): A measure of cosmic time and distance, with higher redshifts corresponding to earlier epochs in the Universe’s history.

Compact galaxy: A galaxy whose stellar half-mass or half-light radius is significantly smaller (often <2 kpc) than typical systems of similar stellar mass in the local Universe.

References

1. Minor Merger Growth in Action: JWST Detects Faint Blue Companions around Massive Quiescent Galaxies at 0.5 ≤ z ≤ 3.0. The Astrophysical Journal Letters (2023).
2. First light and reionization epoch simulations (FLARES) IX: the physical mechanisms driving compact galaxy formation and evolution. Monthly Notices of the Royal Astronomical Society (2023).
3. Rest-frame Near-infrared Sizes of Galaxies at Cosmic Noon: Objects in JWST's Mirror Are Smaller than They Appeared. The Astrophysical Journal Letters (2022).