Turbulent gas-rich discs at high redshift: Chaotic orbits and rapid bulge formation at high gas fraction
Abstract
Using the \nexus\ N-body/hydrodynamic framework, we show that stellar bars that emerge in high-redshift disc galaxies are different in their orbital characteristics compared to their low-redshift counterparts. We identify bar-supporting orbits and, among them, find the fraction of chaotic orbits compared to regular orbits (fchaos). This fraction rises above 60\% for models with fgas > 60 %; for fgas ≲ 60%, we observe chaotic fractions close to zero. The emerging bars seen in the fgas= 80% and 100% simulations collapse in ≲1 Gyr to form central bulges supported by rotation, and this collapse follows soon after the chaotic fraction starts to dominate (fchaos ≳ 50%). Moreover, the gravitational potential in those simulations steepens rapidly over that period, and by integrating the chaotic orbits, we find that orbits that deviate from the evolving mean field are more likely to be chaotic. Hence, we argue that the irregularity associated with the rapidly evolving, central potentials drives higher chaotic fractions in these gas-rich bars. As a result, the emergent bars collapse through `violent relaxation' to form oblate rotating bulges. Supporting evidence for this picture comes from the fact that particles of different mass share identical radial profiles, a natural consequence of the rapid relaxation process.
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BibTeX
@misc{villaalatorre2026turbulent,
title = {{Turbulent gas-rich discs at high redshift: Chaotic orbits and rapid bulge formation at high gas fraction}},
author = {Johan M. Villa-Alatorre and Joss Bland-Hawthorn and Thor Tepper-Garcia and Oscar Agertz and Christoph Federrath},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.38159},
eprint = {2610.38159},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.38159},
}
RIS
TY - UNPB
TI - Turbulent gas-rich discs at high redshift: Chaotic orbits and rapid bulge formation at high gas fraction
AU - Johan M. Villa-Alatorre
AU - Joss Bland-Hawthorn
AU - Thor Tepper-Garcia
AU - Oscar Agertz
AU - Christoph Federrath
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2610.38159
UR - https://arxiv.org/abs/2610.38159
AB - Using the \nexus\ N-body/hydrodynamic framework, we show that stellar bars that emerge in high-redshift disc galaxies are different in their orbital characteristics compared to their low-redshift counterparts. We identify bar-supporting orbits and, among them, find the fraction of chaotic orbits compared to regular orbits (f_chaos). This fraction rises above 60\% for models with f_gas > 60 %; for f_gas ≲ 60%, we observe chaotic fractions close to zero. The emerging bars seen in the f_gas= 80% and 100% simulations collapse in ≲1 Gyr to form central bulges supported by rotation, and this collapse follows soon after the chaotic fraction starts to dominate (f_chaos ≳ 50%). Moreover, the gravitational potential in those simulations steepens rapidly over that period, and by integrating the chaotic orbits, we find that orbits that deviate from the evolving mean field are more likely to be chaotic. Hence, we argue that the irregularity associated with the rapidly evolving, central potentials drives higher chaotic fractions in these gas-rich bars. As a result, the emergent bars collapse through `violent relaxation' to form oblate rotating bulges. Supporting evidence for this picture comes from the fact that particles of different mass share identical radial profiles, a natural consequence of the rapid relaxation process.
ER -