Abstract 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 (0 ≤ z ≤ 8) for galaxies with stellar masses 10⁹\, M, 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 ≈10 K, enabling direct predictions for the atomic (H i) and molecular (H2) KS relations. At z ≈ 0, COLIBRE reproduces the observed (spatially-resolved) KS relations for H i and H2, 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 H2 KS relation shifts to higher normalization in galaxies with higher sSFRs. The H2 depletion time decreases by a factor of ≈20 from z = 0 to z = 8, primarily due to the decreasing gas-phase metallicity. This results in less H2 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 H2 depletion time and its correlation with a galaxy’s sSFR agree remarkably well with observations in a wide redshift range, 0 ≤ z ≤ 5.
Lagos et al. (2026) studied this question.