We present three-dimensional radiation-hydrodynamical simulations of the impact of stellar winds , photoelectric heating , photodissociating and photoionising radiation , and supernovae on the chemical composition and star formation in a stratified disc model .
This is followed with a sink-based model for star clusters with populations of individual massive stars .
Stellar winds and ionising radiation regulate the star formation rate at a factor of \sim 10 below the simulation with only supernova feedback due to their immediate impact on the ambient interstellar medium after star formation .
Ionising radiation ( with winds and supernovae ) significantly reduces the ambient densities for most supernova explosions to \rho < 10 ^ { -25 } g cm ^ { -3 } , compared to 10 ^ { -23 } g cm ^ { -3 } for the model with only winds and supernovae .
Radiation from massive stars reduces the amount of molecular hydrogen and increases the neutral hydrogen mass and volume filling fraction .
Only this model results in a molecular gas depletion time scale of 2 Gyr and shows the best agreement with observations .
In the radiative models , the H \alpha emission is dominated by radiative recombination as opposed to collisional excitation ( the dominant emission in non-radiative models ) , which only contributes \sim 1 – 10 % to the total H \alpha emission .
Individual massive stars ( M \geq 30 M _ { \odot } ) with short lifetimes are responsible for significant fluctuations in the H \alpha luminosities .
The corresponding inferred star formation rates can underestimate the true instantaneous star formation rate by factors of \sim 10 .