Sizes of galaxies from the KMOS^3D^ survey

The stability of the ratio of H{alpha} size to continuum size demonstrates a high degree of stability in halo spin and in the transfer of angular momentum to the disk over a wide range of physical conditions and cosmic time. This may require local regulation by feedback processes. The implication of our results, as we demonstrate using a toy model, is that our upper limit on star-formation-driven growth is sufficient only to evolve star-forming galaxies approximately along the observed size-mass relation, consistent with the size growth of galaxies at constant cumulative comoving number density.

To explain the observed evolution of the size-mass relation of star-forming disk galaxies, other processes, such as the preferential quenching of compact galaxies or galaxy mergers, may be required.