Investigating the H  i mass-size relation using the Simba cosmological simulations

Abstract Observational studies have established a remarkably tight power-law relationship between the H i masses and sizes of late-type galaxies, known as the H i mass-size relation. This relation has been shown to persist across various models of a galaxy‚s H i surface density profile. Using the Simba cosmological simulations, we investigate the robustness of this relation under different feedback prescriptions, including cases where specific feedback mechanisms are absent. While the global properties of galaxies are significantly affected by changes in feedback, the H i mass-size relation remains intact. Moreover, its parameters consistently align with the best available empirical measurements. We analyse the H i mass distributions of galaxies and demonstrate that, regardless of the feedback scenario, galaxies within a given H i mass bin exhibit outer H i radial profiles well-approximated by an exponential function. Furthermore, the exponential decline rate remains remarkably similar across different physical prescriptions. This behaviour is only valid within the ∼ 1 M⊙ pc−2 contour. We attribute the persistence of the H i mass-size relation to this inherent self-similarity in the H i mass distributions.