The properties of central stellar knots embedded in galactic bulges of CIELO simulations
Abstract
Deeply bound stellar substructures of about 1 kpc at the center of bulges are found in a subset of galaxies from the cosmological chemo-hydrodynamical zoom-in CIELO simulation suite. They were identified as stellar overdensities at the lowest binding energies in each galaxy's circularity-energy $(ε, E)$ plane. We refer to these overdensities as stellar knots. We aim to characterize their properties in the context of bulge assembly using CIELO simulated galaxies spanning a wide range of stellar masses (108.0-1010.7 M⊙), with diverse formation histories. We inspect 54 galactic bulges. Within them, we isolate stellar knot candidates in $(ε, E)$ space, and identify 28 robust knots satisfying successive selection criteria: kinematic, concentration, and morphology. We characterize their chemical enrichment, formation timescales, formation sites, progenitor gas origin, and spatial distributions. Across all galaxy masses, knots are systematically alpha-element enhanced, having assembled the bulk of their stellar mass at earlier epochs and on shorter timescales than other bulge populations, with a median of ∼2Gyr versus ∼5Gyr. Regarding their origin, knots are predominantly in-situ (5% accreted mass fraction, roughly half that of the rest of the bulge), with negligible disk-born stars contribution and the largest gas fractions originating from a primordial central spheroid (21% versus 16--17% for the surrounding populations), consistent with being the primary gas fuel for the alpha-element enhancement. In terms of structure, knots exhibit a variety of morphologies, with spheroidal shapes predominating. Dynamical selection in $(ε, E)$ space of CIELO galaxies demonstrates its effectiveness in recovering coeval stellar populations, pointing to stellar knots as plausible fossil signatures of early in-situ bulge assembly.
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BibTeX
@misc{acostatripailao2026properties,
title = {{The properties of central stellar knots embedded in galactic bulges of CIELO simulations}},
author = {Belén Acosta-Tripailao and Patricia B. Tissera and Manuela Zoccali and Jenny Gonzalez-Jara and Brian Tapia-Contreras and Ignacio Muñoz-Escobar and Susana Pedrosa and Nelson D. Padilla and Lucas Bignone and Rosa Dominguez-Tenreiro},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.11465},
eprint = {2609.11465},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.11465},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The properties of central stellar knots embedded in galactic bulges of CIELO simulations
AU - Belén Acosta-Tripailao
AU - Patricia B. Tissera
AU - Manuela Zoccali
AU - Jenny Gonzalez-Jara
AU - Brian Tapia-Contreras
AU - Ignacio Muñoz-Escobar
AU - Susana Pedrosa
AU - Nelson D. Padilla
AU - Lucas Bignone
AU - Rosa Dominguez-Tenreiro
PY - 2026
DA - 2026/09/10
PB - arXiv
DO - 10.48550/arxiv.2609.11465
UR - https://arxiv.org/abs/2609.11465
AB - Deeply bound stellar substructures of about 1 kpc at the center of bulges are found in a subset of galaxies from the cosmological chemo-hydrodynamical zoom-in CIELO simulation suite. They were identified as stellar overdensities at the lowest binding energies in each galaxy's circularity-energy $(ε, E)$ plane. We refer to these overdensities as stellar knots. We aim to characterize their properties in the context of bulge assembly using CIELO simulated galaxies spanning a wide range of stellar masses (10^8.0-10^10.7 M_⊙), with diverse formation histories. We inspect 54 galactic bulges. Within them, we isolate stellar knot candidates in $(ε, E)$ space, and identify 28 robust knots satisfying successive selection criteria: kinematic, concentration, and morphology. We characterize their chemical enrichment, formation timescales, formation sites, progenitor gas origin, and spatial distributions. Across all galaxy masses, knots are systematically alpha-element enhanced, having assembled the bulk of their stellar mass at earlier epochs and on shorter timescales than other bulge populations, with a median of ∼2Gyr versus ∼5Gyr. Regarding their origin, knots are predominantly in-situ (5% accreted mass fraction, roughly half that of the rest of the bulge), with negligible disk-born stars contribution and the largest gas fractions originating from a primordial central spheroid (21% versus 16--17% for the surrounding populations), consistent with being the primary gas fuel for the alpha-element enhancement. In terms of structure, knots exhibit a variety of morphologies, with spheroidal shapes predominating. Dynamical selection in $(ε, E)$ space of CIELO galaxies demonstrates its effectiveness in recovering coeval stellar populations, pointing to stellar knots as plausible fossil signatures of early in-situ bulge assembly.
ER -