Kennicutt–Schmidt relation of galaxies over 13 billion years in the COLIBRE hydrodynamical simulations

We investigate the correlation between star formation rate (SFR) surface density and gas surface density [known as the Kennicutt–Schmidt (KS) relation] at kiloparsec (kpc) scales across cosmic time ((Formula presented) ) for galaxies with stellar masses (Formula presented), using the COLIBRE state-of-the-art cosmological hydrodynamical simulations. These simulations feature on-the-fly non-equilibrium chemistry coupled to dust grain evolution and detailed radiative cooling down to (Formula presented) K, enabling direct predictions for the atomic (H i) and molecular (H(Formula presented) ) KS relations. At (Formula presented), COLIBRE reproduces the observed (spatially resolved) KS relations for H i and H(Formula presented), including the associated scatter, which we predict to be significantly correlated with stellar surface density, local specific SFR (sSFR), and gas metallicity. We show that the H i KS relation steepens for lower-mass galaxies, while the H(Formula presented) KS relation shifts to higher normalization in galaxies with higher sSFRs. The H(Formula presented) depletion time decreases by a factor of (Formula presented) from (Formula presented) to (Formula presented), primarily due to the decreasing gas-phase metallicity. This results in less H(Formula presented) and more H i being associated with a given SFR at higher redshift. We also find that galaxies with higher sSFRs have a larger molecular gas content and higher star formation efficiency per unit gas mass on kpc scales. The predicted evolution of the H(Formula presented) depletion time and its correlation with a galaxy’s sSFR agree remarkably well with observations in a wide redshift range, (Formula presented) .