MIGHTEE-H I: the H I size-mass relation over the last billion years

We present the observed III size-mass relation of 204 galaxies from the MIGIITEE Survey Early Science data. The high sensitivity of MeerKAT allows us to detect galaxies spanning more than 4 orders of magnitude in H I mass, ranging from dwarf galaxies to massive spirals, and including all morphological types. This is the first time the relation has been explored on a blind homogeneous data set that extends over a previously unexplored redshift range of 0 < z < 0.084, i.e. a period of around one billion years in cosmic time. The sample follows the same tight logarithmic relation derived from previous work, between the diameter (D-HI) and the mass (M-HI) of Ht discs. We measure a slope of 0.501 +/- 0.008, an intercept of -3.252(-0.074)(+0.073), and an observed scatter of 0.057 dex. For the first time, we quantify the intrinsic scatter of 0.054 +/- 0.003 dex (similar to 10 per cent), which provides a constraint for cosmological simulations of galaxy formation and evolution. We derive the relation as a function of galaxy type and find that their intrinsic scatters and slopes are consistent within the errors. We also calculate the D-HI-M-HI relation for two redshift bins and do not find any evidence for evolution with redshift. These results suggest that over a period of one billion years in look-back time, galaxy discs have not undergone significant evolution in their gas distribution and mean surface mass density, indicating a lack of dependence on both morphological type and redshift.