On the galaxy-halo connection in the EAGLE simulation

TL;DR

This paper uses the EAGLE simulation to analyze how galaxy size correlates with halo properties, revealing weaker correlations than previously assumed, which improves galaxy formation models.

Contribution

It demonstrates that galaxy sizes have weak correlations with halo properties in EAGLE, challenging common assumptions and aiding more accurate empirical modeling.

Findings

EAGLE galaxies better match observed size and velocity residuals.

Galaxy size correlates weakly with halo mass, concentration, and spin.

Weak correlations improve galaxy scaling predictions.

Abstract

Empirical models of galaxy formation require assumptions about the correlations between galaxy and halo properties. These may be calibrated against observations or inferred from physical models such as hydrodynamical simulations. In this Letter, we use the EAGLE simulation to investigate the correlation of galaxy size with halo properties. We motivate this analysis by noting that the common assumption of angular momentum partition between baryons and dark matter in rotationally supported galaxies overpredicts both the spread in the stellar mass-size relation and the anticorrelation of size and velocity residuals, indicating a problem with the galaxy-halo connection it implies. We find the EAGLE galaxy population to perform significantly better on both statistics, and trace this success to the weakness of the correlations of galaxy size with halo mass, concentration and spin at fixed stellar mass. Using these correlations in empirical models will enable fine-grained aspects of galaxy scalings to be matched.