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Formation and Morphology of the First Galaxies in the Cosmic Morning

Park, Changbom; Lee, Jaehyun; Kim, Juhan; Jeong, Donghui; Pichon, Christophe; Gibson, Brad K.; Snaith, Owain N.; Shin, Jihye; Kim, Yonghwi; Dubois, Yohan; Few, C. Gareth


Changbom Park

Jaehyun Lee

Juhan Kim

Donghui Jeong

Christophe Pichon

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Professor Brad Gibson
Head of Dept, Physics & Maths; Director, E.A. Milne Centre for Astrophysics

Owain N. Snaith

Jihye Shin

Yonghwi Kim

Yohan Dubois


We investigate the formation and morphological evolution of the first galaxies in the cosmic morning (10 ≳ z ≳ 4) using the Horizon Run 5 (HR5) simulation. For galaxies above the stellar mass M ⋆ , min = 2 × 10 9 M ⊙ , we classify them into disk, spheroid, and irregular types according to their asymmetry and stellar-mass morphology. We find that about two-thirds of the galaxies have a Sérsic index <1.5, reflecting the dominance of disk-type morphology in the cosmic morning. The rest are evenly distributed as incidental and transient irregulars or spheroids. These fractions are roughly independent of redshift and stellar mass up to ∼1010 M ⊙. Almost all the first galaxies with M ⋆ > M ⋆ , min at z > 4 form at initial peaks of the matter-density field. Large-scale structures in the universe emerge and grow like cosmic rhizomes as the underlying matter-density fluctuations grow and form associations of galaxies in rare overdense regions and the realm of the galactic world is stretched into relatively lower-density regions along evolving filaments. The cosmic web of galaxies forms at lower redshifts when most rhizomes globally percolate. The primordial angular momentum produced by the induced tidal torques on protogalactic regions is correlated with the internal kinematics of galaxies and tightly aligned with the angular momentum of the total galaxy mass. The large-scale tidal field imprinted in the initial conditions seems responsible for the dominance of disk morphology and for the tendency of galaxies to reacquire a disk postdistortion.


Park, C., Lee, J., Kim, J., Jeong, D., Pichon, C., Gibson, B. K., …Few, C. G. (2022). Formation and Morphology of the First Galaxies in the Cosmic Morning. The Astrophysical journal, 937(1),

Journal Article Type Article
Acceptance Date Jul 27, 2022
Online Publication Date Sep 16, 2022
Publication Date Sep 20, 2022
Deposit Date Dec 10, 2022
Publicly Available Date Dec 15, 2022
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 937
Issue 1
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© 2022. The Author(s). Published by the American Astronomical Society.<br /> Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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