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| Main Authors: | , , , , |
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| Format: | Preprint |
| Published: |
2026
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2602.00626 |
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| _version_ | 1866911631739453440 |
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| author | Chen, Liufei Du, Min Lu, Shuai Li, Jing Ho, Luis C. |
| author_facet | Chen, Liufei Du, Min Lu, Shuai Li, Jing Ho, Luis C. |
| contents | The exponential profile has long been hypothesized as the fundamental morphology of galactic disks. The IllustrisTNG simulations reproduce diverse surface-density profiles: Type I (single exponential), Type II (down-bending), and Type III (up-bending), consistent with observed mass-size relations and kinematics. Type II disks dominate the stellar-mass regime $M_\star < 10^{10.6} M_\odot$ with a prevalence of about 40%, exhibiting systematically extended morphologies. Conversely, Type III and Type I galaxies are more compact while following the same mass-size scaling relation. Evolutionary histories show that Type II galaxies experience minimal external perturbations, suggesting that Type II disks represent an intrinsic disk form and challenging conventional single-exponential paradigms. We demonstrate that Type II breaks arise naturally via inside-out growth since $z=1$, governed by synchronized cold-gas accretion and localized peaks in specific star formation rate. This mechanism also produces the characteristic U-shaped age profiles of Type II disks. Stellar dynamical redistribution plays a minor role in their formation. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2602_00626 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Down-bending Breaks in Galactic Disks Are an Intrinsic Byproduct of Inside-out Growth Chen, Liufei Du, Min Lu, Shuai Li, Jing Ho, Luis C. Astrophysics of Galaxies The exponential profile has long been hypothesized as the fundamental morphology of galactic disks. The IllustrisTNG simulations reproduce diverse surface-density profiles: Type I (single exponential), Type II (down-bending), and Type III (up-bending), consistent with observed mass-size relations and kinematics. Type II disks dominate the stellar-mass regime $M_\star < 10^{10.6} M_\odot$ with a prevalence of about 40%, exhibiting systematically extended morphologies. Conversely, Type III and Type I galaxies are more compact while following the same mass-size scaling relation. Evolutionary histories show that Type II galaxies experience minimal external perturbations, suggesting that Type II disks represent an intrinsic disk form and challenging conventional single-exponential paradigms. We demonstrate that Type II breaks arise naturally via inside-out growth since $z=1$, governed by synchronized cold-gas accretion and localized peaks in specific star formation rate. This mechanism also produces the characteristic U-shaped age profiles of Type II disks. Stellar dynamical redistribution plays a minor role in their formation. |
| title | Down-bending Breaks in Galactic Disks Are an Intrinsic Byproduct of Inside-out Growth |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2602.00626 |