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

In the standard disc galaxy formation model, the sizes of galactic discs are tightly related to the spin parameters lambda of their dark matter haloes. The model has been wildly adopted by various semi-analytical 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 disc galaxies and compare it with a popular disc galaxy formation model of Mo et al. (). Intriguingly, galactic sizes correlate 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 overall 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 parameter relation, which will be explored in our future work.