The Galaxy Stellar Mass–Star Formation Rate–Size Relation in EAGLE, TNG100, and Observations

Jiani Chu; Dandan Xu; Enci Wang; Stijn Wuyts

doi:10.3847/1538-4357/ae7433

The Galaxy Stellar Mass–Star Formation Rate–Size Relation in EAGLE, TNG100, and Observations

Jiani Chu
, Dandan Xu
, Enci Wang
, Stijn Wuyts

Tsinghua University
Hefei University of Technology

Research output: Contribution to journal › Article › peer-review

Abstract

The stellar mass, size, and star formation rate (SFR) are fundamental properties that encode the structural and evolutionary states of galaxies. Observations reveal a mass–SFR–size relation, whereby galaxies become more compact both above and below the ridge of the star-forming main sequence (SFMS), linking galaxy structure to star formation activity. We investigate this relation by comparing galaxies from two cosmological hydrodynamical simulations, EAGLE and TNG100, with observational samples from the Sloan Digital Sky Survey and CANDELS over three redshift intervals (0 ≤ z < 0.2, 0.5 ≤ z < 1.5, and 1.5 ≤ z < 2.5). Both simulations reproduce the observed trend of galaxy sizes decreasing with increasing offset away from the SFMS. This trend, however, weakens and is not detected in the observational sample at 1.5 < z < 2.5, likely due to increased measurement uncertainties. In contrast, the trend persists in both simulations up to z = 2.5. Across all redshifts, EAGLE predicts a stronger size dependence on the SFMS offset than observed, whereas TNG100 exhibits a weaker dependence. We discuss how this mass–SFR–size relation can be understood in terms of different time variability in SFR across the SFMS.

Original language	English
Article number	67
Journal	Astrophysical Journal
Volume	1005
Issue number	1
Early online date	25 Jun 2026
DOIs	https://doi.org/10.3847/1538-4357/ae7433
Publication status	Published - 1 Jul 2026

Funding

We thank Yuqian Gui and Drs. Lizhi Xie and Lan Wang for useful discussion. We also thank an anonymous referee for useful and constructive comments. This work is supported by the National Key Research and Development Program of China (grant No. 2022YFA1602903), the National Natural Science Foundation of China (grant Nos. 12433003 and 12473008), and the China Manned Space Project (No. CMSCSST-2025-A10). The authors gratefully acknowledge support from the Royal Society International Exchanges scheme (IES\R2\242195). S.W. acknowledges support from China’s National Foreign Expert program (H20240871). This work acknowledges the Tsinghua Astrophysics High-Performance Computing platform for providing the computational and storage resources that supported this research.

Keywords

Galaxy properties (615)
Magnetohydrodynamical simulations (1966)

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.3847/1538-4357/ae7433Licence: CC BY

Cite this

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abstract = "The stellar mass, size, and star formation rate (SFR) are fundamental properties that encode the structural and evolutionary states of galaxies. Observations reveal a mass–SFR–size relation, whereby galaxies become more compact both above and below the ridge of the star-forming main sequence (SFMS), linking galaxy structure to star formation activity. We investigate this relation by comparing galaxies from two cosmological hydrodynamical simulations, EAGLE and TNG100, with observational samples from the Sloan Digital Sky Survey and CANDELS over three redshift intervals (0 ≤ z < 0.2, 0.5 ≤ z < 1.5, and 1.5 ≤ z < 2.5). Both simulations reproduce the observed trend of galaxy sizes decreasing with increasing offset away from the SFMS. This trend, however, weakens and is not detected in the observational sample at 1.5 < z < 2.5, likely due to increased measurement uncertainties. In contrast, the trend persists in both simulations up to z = 2.5. Across all redshifts, EAGLE predicts a stronger size dependence on the SFMS offset than observed, whereas TNG100 exhibits a weaker dependence. We discuss how this mass–SFR–size relation can be understood in terms of different time variability in SFR across the SFMS.",

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The Galaxy Stellar Mass–Star Formation Rate–Size Relation in EAGLE, TNG100, and Observations

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