The Galaxy Stellar Mass-SFR-Size Relation in EAGLE, TNG100, and Observations

TL;DR

This study compares galaxy size, mass, and star formation rate relations in simulations and observations across different redshifts, revealing that simulations reproduce observed trends but with varying strength, providing insights into galaxy evolution.

Contribution

It is the first comprehensive comparison of the mass-SFR-size relation in EAGLE, TNG100 simulations, and observational data across multiple redshifts, highlighting differences in size dependence on star formation activity.

Findings

Simulations reproduce the trend of decreasing galaxy size with increased offset from the SFMS.

The trend weakens at higher redshift in observations but persists in simulations up to z=2.5.

EAGLE predicts a stronger size dependence on SFMS offset than TNG100 or observations.

Abstract

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 SDSS 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 that galaxy sizes decrease 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 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 star formation rate across the SFMS.