MIGHTEE-H I: the MHI - M relation over the last billion years

We study the M-H I - M-star relation over the last billion years using the MIGHTEE-H I sample. We first model the upper envelope of the M-H I - M-star relation with a Bayesian technique applied to a total number of 249 H I-selected galaxies, without binning the data sets, while taking account of the intrinsic scatter. We fit the envelope with both linear and non-linear models, and find that the non-linear model is preferred over the linear one with a measured transition stellar mass of log 10 (M-star/M-circle dot) = 9.15 +/- 0.87, beyond which the slope flattens. This finding supports the view that the lack of H I gas is ultimately responsible for the decreasing star formation rate observed in the massive main-sequence galaxies. For spirals alone, which are biased towards the massive galaxies in our sample, the slope beyond the transition mass is shallower than for the full sample, indicative of distinct gas processes ongoing for the spirals/high-mass galaxies from other types with lower stellar masses. We then create mock catalogues for the MIGHTEE-H I detections and non-detections with two main galaxy populations of late- and early-type galaxies to measure the underlying M-H I - M-star relation. We find that the turnover in this relation persists whether considering the two galaxy populations as a whole or separately. We note that an underlying linear relation could mimic this turnover in the observed scaling relation, but a model with a turnover is strongly preferred. Measurements on the logarithmic average of H I masses against the stellar mass are provided as a benchmark for future studies.