We use hydrodynamical simulations from the OWLS project to investigate the dependence of the physical properties of galaxy populations at redshift 2 on metal-line cooling and feedback from star formation and active galactic nuclei ( AGN ) .
We find that if the sub-grid feedback from star formation is implemented kinetically , the feedback is only efficient if the initial wind velocity exceeds a critical value .
This critical velocity increases with galaxy mass and also if metal-line cooling is included .
This suggests that radiative losses quench the winds if their initial velocity is too low .
If the feedback is efficient , then the star formation rate is inversely proportional to the amount of energy injected per unit stellar mass formed ( which is proportional to the initial mass loading for a fixed wind velocity ) .
This can be understood if the star formation is self-regulating , i.e .
if the star formation rate ( and thus the gas fraction ) increase until the outflow rate balances the inflow rate .
Feedback from AGN is efficient at high masses , while increasing the initial wind velocity with gas pressure or halo mass allows one to generate galaxy-wide outflows at all masses .
Matching the observed galaxy mass function requires efficient feedback .
In particular , the predicted faint-end slope is too steep unless we resort to highly mass loaded winds for low-mass objects .
Such efficient feedback from low-mass galaxies ( M _ { \ast } \ll 10 ^ { 10 } { M } _ { \odot } ) also reduces the discrepancy with the observed specific star formation rates , which are higher than predicted unless the feedback transitions from highly efficient to inefficient just below M _ { \ast } \sim 5 \times 10 ^ { 9 } M _ { \odot } .