Turbulent gas-rich discs at high redshift: the origin of early massive stellar bars
Abstract
Recent observations combining the power of ALMA and JWST have revealed large (3−7 kpc), massive (3−10×1010 M⊙) stellar bars at z=4−5 when the Universe was only 1.2-1.6 Gyr old. At this early epoch, the host galaxy was baryon-dominated (typically 75\% gas, 25\% stars) within the observed extent of the disc (8−15 kpc). Using NEXUS N-body/hydrodynamic simulations, we show that such bars can form promptly (400−800 Myr), provided the disc mass fraction is high (fdisc≳ 70%) and the bar is gas-dominated at the time of its formation, consistent with the observations. In this limit, gas-free bars are unstable to vertical bending modes, but a dominant gas component suppresses this instability. Unlike massive bars in the local Universe, these early bars were sites of vigorous star formation, as we show. Remarkably, for gas-rich models with fgas≲60%, the bars develop X-shaped boxy bulges; at higher gas fractions (fgas> 60%), diffusion suppresses resonant orbit trapping and the emerging bar collapses within 1 Gyr to form a classical bulge. The bar formation time, length, mass, and m=2 Fourier amplitude are all inversely related to fgas. We present a simple analytic model for how stochastic forcing shifts the bar onset time, defined as the time at which the growing bar amplitude reaches a specified threshold.
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BibTeX
@misc{blandhawthorn2026turbulent,
title = {{Turbulent gas-rich discs at high redshift: the origin of early massive stellar bars}},
author = {Joss Bland-Hawthorn and Thor Tepper-Garcia and Chris Hamilton and Johan M. Villa-Alatorre and Oscar Agertz and Takafumi Tsukui and Ken Freeman},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.03275},
eprint = {2609.03275},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.03275},
}
RIS
TY - UNPB
TI - Turbulent gas-rich discs at high redshift: the origin of early massive stellar bars
AU - Joss Bland-Hawthorn
AU - Thor Tepper-Garcia
AU - Chris Hamilton
AU - Johan M. Villa-Alatorre
AU - Oscar Agertz
AU - Takafumi Tsukui
AU - Ken Freeman
PY - 2026
DA - 2026/09/03
PB - arXiv
DO - 10.48550/arxiv.2609.03275
UR - https://arxiv.org/abs/2609.03275
AB - Recent observations combining the power of ALMA and JWST have revealed large (3−7 kpc), massive (3−10×10^10 M_⊙) stellar bars at z=4−5 when the Universe was only 1.2-1.6 Gyr old. At this early epoch, the host galaxy was baryon-dominated (typically 75\% gas, 25\% stars) within the observed extent of the disc (8−15 kpc). Using NEXUS N-body/hydrodynamic simulations, we show that such bars can form promptly (400−800 Myr), provided the disc mass fraction is high (f_disc≳ 70%) and the bar is gas-dominated at the time of its formation, consistent with the observations. In this limit, gas-free bars are unstable to vertical bending modes, but a dominant gas component suppresses this instability. Unlike massive bars in the local Universe, these early bars were sites of vigorous star formation, as we show. Remarkably, for gas-rich models with f_gas≲60%, the bars develop X-shaped boxy bulges; at higher gas fractions (f_gas> 60%), diffusion suppresses resonant orbit trapping and the emerging bar collapses within 1 Gyr to form a classical bulge. The bar formation time, length, mass, and m=2 Fourier amplitude are all inversely related to f_gas. We present a simple analytic model for how stochastic forcing shifts the bar onset time, defined as the time at which the growing bar amplitude reaches a specified threshold.
ER -