Beyond the Disc--Spheroid Dichotomy at 0.6 < z < 8.0: Evidence for a Morphological Indeterminacy Regime from JWST
Abstract
Galaxy morphology is a fundamental tracer of galaxy assembly, but its characterization becomes increasingly uncertain in the early Universe. We investigate morphological classifications across different methodologies over the redshift range 0.6 < z < 8.0, using JWST observations of 15,567 galaxies with 6,099 synthetic galaxies from IllustrisTNG. To quantify morphology without relying on visual labels or prescribed light profiles, we use an unsupervised-supervised hybrid machine-learning approach based on the non-parametric MEGG system, which combines the second moment of the light distribution, Entropy, Gini, and Gradient Pattern Analysis. We find that parametric and non-parametric classifications remain broadly consistent at z < 2.5, but diverge systematically at higher redshift. We identify this epoch as the Morphological Indeterminacy Regime (MIR), in which classical disc and spheroidal categories no longer provide a unique description of the galaxy population. The fraction of mixed-interpretation galaxies increases with redshift, reaching FMIR ∼ 0.55 at z > 2.5. Cross-domain and projection-invariance tests show that the classifications are stable and insensitive to data set and viewing angle. In the interval 2.5 < z < 8.0, MIR galaxies occupy an intermediate stellar-mass regime (median; log(M⋆/M⊙) ∼ 9.7), between low-mass discs (median; log(M⋆/M⊙) ∼ 9.5) and massive spheroids (median; log(M⋆/M⊙) ∼ 10.1), while irregular systems have stellar-mass distributions similar to those of MIR galaxies. We interpret these results as evidence that morphological indeterminacy is a characteristic feature of galaxy assembly in the early Universe, reflecting a population of dynamically young systems that have not yet settled into the classical Hubble sequence.
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BibTeX
@misc{kolesnikov2026beyond,
title = {{Beyond the Disc--Spheroid Dichotomy at $0.6 < z < 8.0$: Evidence for a Morphological Indeterminacy Regime from JWST}},
author = {Igor Kolesnikov and Reinaldo Ramos de Carvalho and Jeong Hwan Lee and Rodrigo Flores-Freitas and Vitor M. Sampaio and Luiz A. Silva-Lima},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.24078},
eprint = {2610.24078},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.24078},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Beyond the Disc--Spheroid Dichotomy at 0.6 < z < 8.0: Evidence for a Morphological Indeterminacy Regime from JWST
AU - Igor Kolesnikov
AU - Reinaldo Ramos de Carvalho
AU - Jeong Hwan Lee
AU - Rodrigo Flores-Freitas
AU - Vitor M. Sampaio
AU - Luiz A. Silva-Lima
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.24078
UR - https://arxiv.org/abs/2610.24078
AB - Galaxy morphology is a fundamental tracer of galaxy assembly, but its characterization becomes increasingly uncertain in the early Universe. We investigate morphological classifications across different methodologies over the redshift range 0.6 < z < 8.0, using JWST observations of 15,567 galaxies with 6,099 synthetic galaxies from IllustrisTNG. To quantify morphology without relying on visual labels or prescribed light profiles, we use an unsupervised-supervised hybrid machine-learning approach based on the non-parametric MEGG system, which combines the second moment of the light distribution, Entropy, Gini, and Gradient Pattern Analysis. We find that parametric and non-parametric classifications remain broadly consistent at z < 2.5, but diverge systematically at higher redshift. We identify this epoch as the Morphological Indeterminacy Regime (MIR), in which classical disc and spheroidal categories no longer provide a unique description of the galaxy population. The fraction of mixed-interpretation galaxies increases with redshift, reaching F_MIR ∼ 0.55 at z > 2.5. Cross-domain and projection-invariance tests show that the classifications are stable and insensitive to data set and viewing angle. In the interval 2.5 < z < 8.0, MIR galaxies occupy an intermediate stellar-mass regime (median; log(M_⋆/M_⊙) ∼ 9.7), between low-mass discs (median; log(M_⋆/M_⊙) ∼ 9.5) and massive spheroids (median; log(M_⋆/M_⊙) ∼ 10.1), while irregular systems have stellar-mass distributions similar to those of MIR galaxies. We interpret these results as evidence that morphological indeterminacy is a characteristic feature of galaxy assembly in the early Universe, reflecting a population of dynamically young systems that have not yet settled into the classical Hubble sequence.
ER -