Using a sample of 67 galaxies from the MIGHTEE Survey Early Science data we study the H i-based baryonic Tully-Fisher relation (bTFr), covering a period of ∼one billion years (0 ≤ z ≤ 0.081). We consider the bTFr based on two different rotational velocity measures: the width of the global H i profile and Vout, measured as the outermost rotational velocity from the resolved H i rotation curves. Both relations exhibit very low intrinsic scatter orthogonal to the best-fit relation (σ⊥ = 0.07 ± 0.01), comparable to the SPARC sample at z ≃ 0. The slopes of the relations are similar and consistent with the z ≃ 0 studies ($3.66^{+0.35}_{-0.29}$ for W50 and $3.47^{+0.37}_{-0.30}$ for Vout). We find no evidence that the bTFr has evolved over the last billion years, and all galaxies in our sample are consistent with the same relation independent of redshift and the rotational velocity measure. Our results set up a reference for all future studies of the H i-based bTFr as a function of redshift that will be conducted with the ongoing deep SKA pathfinders surveys.

We present the first measurements of H i galaxy scaling relations from a blind survey at z > 0.15. We perform spectral stacking of 9023 spectra of star-forming galaxies undetected in H i at 0.23 < z < 0.49, extracted from MIGHTEE-H i Early Science data cubes, acquired with the MeerKAT radio telescope. We stack galaxies in bins of galaxy properties (stellar mass M *, star formation rateSFR, and specific star formation rate sSFR, with sSFR ≡ M */SFR), obtaining ≳5σ detections in most cases, the strongest H i-stacking detections to date in this redshift range. With these detections, we are able to measure scaling relations in the probed redshift interval, finding evidence for a moderate evolution from the median redshift of our sample z med ∼ 0.37 to z ∼ 0. In particular, low-M * galaxies ( log 10 ( M * / M ⊙ ) ∼ 9 ) experience a strong H i depletion (∼0.5 dex in log 10 ( M H I / M ⊙ ) ), while massive galaxies ( log 10 ( M * / M ⊙ ) ∼ 11 ) keep their H i mass nearly unchanged. When looking at the star formation activity, highly star-forming galaxies evolve significantly in M H I (f H I, where f H I ≡ M H I/M *) at fixed SFR (sSFR), while at the lowest probed SFR (sSFR) the scaling relations show no evolution. These findings suggest a scenario in which low-M * galaxies have experienced a strong H i depletion during the last ∼5 Gyr, while massive galaxies have undergone a significant H i replenishment through some accretion mechanism, possibly minor mergers. Interestingly, our results are in good agreement with the predictions of the simba simulation. We conclude that this work sets novel important observational constraints on galaxy scaling relations.

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