The galaxy size to halo spin relation of disk galaxies in cosmological hydrodynamical simulations

TL;DR

This study investigates the relationship between galaxy sizes and halo spin parameters in cosmological hydrodynamical simulations, revealing a strong correlation in some simulations but not others, challenging existing models.

Contribution

It provides the first large-sample analysis of the size-spin relation in hydrodynamical simulations, comparing results with the Mo et al. (1998) model and highlighting discrepancies.

Findings

Strong size-spin correlation in IllustrisTNG simulations.

Weaker or no correlation in EAGLE dwarf galaxies.

Discrepancies with the Mo et al. (1998) model predictions.

Abstract

In the standard disk galaxy formation model, the sizes of galactic disks are tightly related to the spin parameters $\lambda$ of their dark matter haloes. The model has been wildly adopted by various semi-analytic galaxy formation models which have been extremely successful to interpret a large body of observational data. However, the size-$\lambda$ correlation was rarely seen in most modern hydrodynamical simulations of galaxy formation. In this short paper, we make use of 4 sets of large hydrodynamical simulations to explore the size-spin parameter relation with a large sample of simulated disk galaxies, and compare it with a popular disk galaxy formation model of Mo et al. (1998). Intriguingly, galactic sizes correlate strongly with spin parameters of their dark matter haloes in the simulations developed by the IllustrisTNG collaborations, albeit the relation does not always agree with prediction of MMW98 model over all stellar mass range we examined. There is also a size-spin correlation for the Milky way analogies in the EAGLE simulations, while it is relatively weaker than that of the IllustrisTNG counterparts. For the dwarfs in the simulations from the EAGLE collaboration, there is NULL correlation. We conclude that either the detailed subgrid physics or hydrodynamics solvers account for the size-spin relation, which will be explored in our future work.