The drivers of cosmic dust temperature evolution

Context. Observations of the rest-frame far-infrared (far-IR) emission of galaxies suggest a mild increase in dust temperature T-dust with redshift. However, constraining T-dust in high-redshift systems remains challenging due to limited sampling of the far-IR spectral energy distribution (SED). Aims. We present and discuss the redshift evolution of T-dust, predicted by a cosmological galaxy evolution simulation with dust treatment, and interpret its dependence on other galaxy physical properties. Methods. We used a semi-analytic model of galaxy formation that includes an explicit treatment of dust, post-processed with radiative transfer. Dust temperatures were derived by applying modified blackbody SED fitting to the simulated galaxies, mirroring the methodology adopted in most observational studies. Results. The dust temperature of our simulated galaxies increases with redshift, in broad agreement with observational results. A feature-importance analysis reveals that the star formation rate surface density Sigma(SFR) and the dust-to-gas ratio (DTG) are the main drivers of dust temperature, tracing the intensity of the interstellar radiation field and the optical depth of warm molecular clouds, respectively. Galaxies with higher star formation rate surface densities and lower DTGs - common conditions at high-z - are associated with warmer dust. We provide a simple relation to estimate DTG from Sigma(SFR), T-dust, and redshift. Variations in dust grain size and chemical composition have a negligible impact on T-dust. Our results are particularly relevant to the study of dust properties in observations of high-z galaxies, where far-IR dust emission is not fully sampled.