A stellar bar hidden in an extreme gas-rich disk galaxy at z=4.055
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| Natura: | Preprint |
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2026
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| author | Boogaard, Leindert A. Costantin, Luca Tepper-García, Thor Bland-Hawthorn, Joss Hodge, Jacqueline A. Liao, Cheng-Lin Hamed, Mahmoud Colina, Luis Walter, Fabian Agertz, Oscar Bik, Arjan Gómez, Alejandro Crespo Daddi, Emanuele Magdis, Georgios E. Pérez-González, Pablo G. Übler, Hannah Weiss, Axel |
| author_facet | Boogaard, Leindert A. Costantin, Luca Tepper-García, Thor Bland-Hawthorn, Joss Hodge, Jacqueline A. Liao, Cheng-Lin Hamed, Mahmoud Colina, Luis Walter, Fabian Agertz, Oscar Bik, Arjan Gómez, Alejandro Crespo Daddi, Emanuele Magdis, Georgios E. Pérez-González, Pablo G. Übler, Hannah Weiss, Axel |
| contents | The classical picture for the formation of stellar bars -- key dynamical drivers of the evolution of galaxies -- is through secular evolution of instability in gas poor, stellar-dominated disks. The detection with the James Webb Space Telescope (JWST) of stellar bars and spiral arms in galaxies at early cosmic times has thus challenged LambdaCDM-based expectations, which recent studies reconcile by suggesting that these galaxies are baryon-dominated and have already consumed most of their gas. Yet, a paradox arises, as early galaxies are expected to be increasingly rich in gas, which is generally considered to prevent or slow down stellar bar formation. Here, we show the detection of a stellar bar in GN20, a gas-rich star-forming disk galaxy at a redshift of z=4.055, only 1.5 billion years after the Big Bang. Simultaneous observations of the stars, gas, and dust reveal that GN20 is indeed baryon-dominated (over dark matter; 70+/-30%), but the baryonic mass is largely in the form of gas (75+/-25%). This discovery demonstrates that gas-rich disks do support rapid stellar bar formation in the early Universe, motivating a new theoretical perspective on bar formation in gas-rich systems, and providing a potential new mechanism for very early galaxy assembly and quenching. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_15273 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | A stellar bar hidden in an extreme gas-rich disk galaxy at z=4.055 Boogaard, Leindert A. Costantin, Luca Tepper-García, Thor Bland-Hawthorn, Joss Hodge, Jacqueline A. Liao, Cheng-Lin Hamed, Mahmoud Colina, Luis Walter, Fabian Agertz, Oscar Bik, Arjan Gómez, Alejandro Crespo Daddi, Emanuele Magdis, Georgios E. Pérez-González, Pablo G. Übler, Hannah Weiss, Axel Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics The classical picture for the formation of stellar bars -- key dynamical drivers of the evolution of galaxies -- is through secular evolution of instability in gas poor, stellar-dominated disks. The detection with the James Webb Space Telescope (JWST) of stellar bars and spiral arms in galaxies at early cosmic times has thus challenged LambdaCDM-based expectations, which recent studies reconcile by suggesting that these galaxies are baryon-dominated and have already consumed most of their gas. Yet, a paradox arises, as early galaxies are expected to be increasingly rich in gas, which is generally considered to prevent or slow down stellar bar formation. Here, we show the detection of a stellar bar in GN20, a gas-rich star-forming disk galaxy at a redshift of z=4.055, only 1.5 billion years after the Big Bang. Simultaneous observations of the stars, gas, and dust reveal that GN20 is indeed baryon-dominated (over dark matter; 70+/-30%), but the baryonic mass is largely in the form of gas (75+/-25%). This discovery demonstrates that gas-rich disks do support rapid stellar bar formation in the early Universe, motivating a new theoretical perspective on bar formation in gas-rich systems, and providing a potential new mechanism for very early galaxy assembly and quenching. |
| title | A stellar bar hidden in an extreme gas-rich disk galaxy at z=4.055 |
| topic | Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2605.15273 |