IRX (ratio of IR to UV 1550 Å luminosity) as a function of stellar mass (left panel) and UV stellar continuum slope (middle panel). Galaxies with spatially resolved morphology in F1500W are colour-coded by their Σ_SFR. A linear fit to log(IRX)−log(M_*/M_⊙) is shown in the left panel (slope of 0.96 ± 0.06 and intercept of −8.47 ± 0.61). In the middle panel, we show three IRX-β relations in the literature adopted from Reddy et al. (2018) assuming a constant star formation history and an age of 100 Myr for stellar populations: the original Meurer et al. (1999) relation, the starburst curve of Calzetti et al. (2000) and the SMC curve of Gordon et al. (2003) assuming 0.14 Solar metallicity. A higher metallicity system will result in a redder intrinsic UV slope (β₀), shifting the curves to the right of the diagram (e.g. the Calzetti curve for a 1.4 Z_⊙ population and β₀ = −2.4 resembles the Meurer et al. 1999 curve). Galaxies with higher Σ_SFR at a given mass or β have higher IRX and a shallower attenuation curve. Right panel: V-band dust optical depth versus Σ_SFR, colour-coded with the attenuation curve slope defined as the deviation from the Calzetti et al. (2000) (the formalism of Kriek & Conroy 2013), where zero is the Calzetti curve slope. The two parameters are highly correlated with ρ = 0.65 (p-value ≪ 1). The shallower attenuation curve of galaxies with high IRX at a given mass or β can be explained by the radiative transfer effects that are a result of their high Σ_SFR: higher optical depths and lower fractions of unobscured evolved stars.