Transforming galaxies with EASE: widespread structural changes enabled by short-lived spirals
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arXiv
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| Format: | Preprint |
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2025
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| author | van der Wel, Arjen Meidt, Sharon E. |
| author_facet | van der Wel, Arjen Meidt, Sharon E. |
| contents | We propose that galaxy structural changes - and the rapid rise of a population of galaxies with early-type morphologies at cosmic noon ($1<z<3$) - can be explained with EASE: Early, Accelerated, Secular Evolution. The mechanism relies on the torques exerted by stellar spirals in late-type galaxies that are present and active at $z>1.5$ as revealed by JWST/NIRCam. The process is at once secular, because the transformative structural changes (heating, compaction, bulge formation) occur over many ($\approx10-30$) orbital periods, but accelerated, because orbital times were significantly shorter than at the present day. In a first application, we take galaxy effective radius as a proxy for galaxy structure and, using new measurements of the abundance and properties of stellar spirals observed in a collection of JWST deep fields, show that EASE predicts a distribution of early-type sizes that is smaller than late-type galaxies and consistent with what is observed. The success of EASE relies on an updated picture of the influence of spiral arms, in which transience plays a key role. We present a new calculation of the characteristic wave equation in the fluid approximation that applies to steady and non-steady open spirals beyond the more traditional tight-winding limit. This shows open, transient spirals above the Jeans length growing and decaying on the order of a dynamical time in a wider region around and inside corotation than canonical steady spirals. We show that this transient activity spreads out angular momentum gains and losses, and the associated dynamical heating, giving spirals a more extended influence than a single steady spiral. The ubiquity of spirals in star-forming galaxies with $M_*>10^{10.5}M_{\odot}$ across the redshifts where early-type galaxies appear in large numbers suggests that EASE can play an important role in the morphological transformation of galaxies. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_02847 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Transforming galaxies with EASE: widespread structural changes enabled by short-lived spirals van der Wel, Arjen Meidt, Sharon E. Astrophysics of Galaxies We propose that galaxy structural changes - and the rapid rise of a population of galaxies with early-type morphologies at cosmic noon ($1<z<3$) - can be explained with EASE: Early, Accelerated, Secular Evolution. The mechanism relies on the torques exerted by stellar spirals in late-type galaxies that are present and active at $z>1.5$ as revealed by JWST/NIRCam. The process is at once secular, because the transformative structural changes (heating, compaction, bulge formation) occur over many ($\approx10-30$) orbital periods, but accelerated, because orbital times were significantly shorter than at the present day. In a first application, we take galaxy effective radius as a proxy for galaxy structure and, using new measurements of the abundance and properties of stellar spirals observed in a collection of JWST deep fields, show that EASE predicts a distribution of early-type sizes that is smaller than late-type galaxies and consistent with what is observed. The success of EASE relies on an updated picture of the influence of spiral arms, in which transience plays a key role. We present a new calculation of the characteristic wave equation in the fluid approximation that applies to steady and non-steady open spirals beyond the more traditional tight-winding limit. This shows open, transient spirals above the Jeans length growing and decaying on the order of a dynamical time in a wider region around and inside corotation than canonical steady spirals. We show that this transient activity spreads out angular momentum gains and losses, and the associated dynamical heating, giving spirals a more extended influence than a single steady spiral. The ubiquity of spirals in star-forming galaxies with $M_*>10^{10.5}M_{\odot}$ across the redshifts where early-type galaxies appear in large numbers suggests that EASE can play an important role in the morphological transformation of galaxies. |
| title | Transforming galaxies with EASE: widespread structural changes enabled by short-lived spirals |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2509.02847 |