The assembly of bulge-dominated galaxies: two evolutionary channels traced through morphology, kinematics, and environment with a hybrid classification pipeline
Abstract
We investigate the physical origin of the bimodality in bulge-dominated galaxies, originally identified by Sampaio et al. (2025), by combining non-parametric morphological metrics, structural scaling relations, stellar kinematics, and environmental trends across a wide redshift range (0.2 < z < 2.4). Using the MEGG-based hybrid classification pipeline applied to CANDELS imaging, we examine the distributions of morphological metrics for two families of bulge-dominated galaxies: G1, with high specific star formation rate (sSFR) distributions, similar to discs, and G2 with lower sSFR. We find that G1 galaxies occupy an intermediate position between discs and G2 spheroids in morphological metrics, and this behaviour persists up to z = 1.4. Fitting the Kormendy relation separately for each family, we find a persistent offset in the zero-point across all redshifts: G2 galaxies are systematically brighter in mean effective surface brightness at fixed effective radius, likely indicating higher central stellar densities. This offset is present in both observed and rest-frame magnitudes, and we argue that it reflects a genuine difference in assembly history. A cross-match with MUSE observations reveals that G1 galaxies have higher projected angular momentum than G2 galaxies, with G1 galaxies overlapping with the disc population, while G2 galaxies are more dispersion-dominated. The redshift evolution of morphological fractions shows that, at high stellar masses, the G2 fraction grows, while discs follow the opposite trend. In parallel, G1 remains a stable, lower-mass population consistent with secular bulge growth. Finally, within galaxy clusters, G1 galaxies are preferentially found at larger cluster-centric radii, suggesting that high-density environments amplify the bimodality by accelerating quenching.
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BibTeX
@misc{floresfreitas2026assembly,
title = {{The assembly of bulge-dominated galaxies: two evolutionary channels traced through morphology, kinematics, and environment with a hybrid classification pipeline}},
author = {R. Flores-Freitas and R. R. de Carvalho and K. V. Nedkova and I. Ferreras and I. Kolesnikov and V. M. Sampaio},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.23246},
eprint = {2609.23246},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.23246},
}
RIS
TY - UNPB
TI - The assembly of bulge-dominated galaxies: two evolutionary channels traced through morphology, kinematics, and environment with a hybrid classification pipeline
AU - R. Flores-Freitas
AU - R. R. de Carvalho
AU - K. V. Nedkova
AU - I. Ferreras
AU - I. Kolesnikov
AU - V. M. Sampaio
PY - 2026
DA - 2026/09/19
PB - arXiv
DO - 10.48550/arxiv.2609.23246
UR - https://arxiv.org/abs/2609.23246
AB - We investigate the physical origin of the bimodality in bulge-dominated galaxies, originally identified by Sampaio et al. (2025), by combining non-parametric morphological metrics, structural scaling relations, stellar kinematics, and environmental trends across a wide redshift range (0.2 < z < 2.4). Using the MEGG-based hybrid classification pipeline applied to CANDELS imaging, we examine the distributions of morphological metrics for two families of bulge-dominated galaxies: G1, with high specific star formation rate (sSFR) distributions, similar to discs, and G2 with lower sSFR. We find that G1 galaxies occupy an intermediate position between discs and G2 spheroids in morphological metrics, and this behaviour persists up to z = 1.4. Fitting the Kormendy relation separately for each family, we find a persistent offset in the zero-point across all redshifts: G2 galaxies are systematically brighter in mean effective surface brightness at fixed effective radius, likely indicating higher central stellar densities. This offset is present in both observed and rest-frame magnitudes, and we argue that it reflects a genuine difference in assembly history. A cross-match with MUSE observations reveals that G1 galaxies have higher projected angular momentum than G2 galaxies, with G1 galaxies overlapping with the disc population, while G2 galaxies are more dispersion-dominated. The redshift evolution of morphological fractions shows that, at high stellar masses, the G2 fraction grows, while discs follow the opposite trend. In parallel, G1 remains a stable, lower-mass population consistent with secular bulge growth. Finally, within galaxy clusters, G1 galaxies are preferentially found at larger cluster-centric radii, suggesting that high-density environments amplify the bimodality by accelerating quenching.
ER -