LAUSR

We present the first measurement of the H i mass function (HIMF) using data from MeerKAT, based on 276 direct detections from the MIGHTEE Survey Early Science data covering a period of approximately a billion years (0 ≤ z ≤ 0.084). This is the first HIMF measured using interferometric data over non-group or cluster field, i.e. a deep blank field. We constrain the parameters of the Schechter function which describes the HIMF with two different methods: $1/\rm V_{\rm max}$ and Modified Maximum Likelihood (MML). We find a low-mass slope $\alpha =-1.29^{+0.37}_{-0.26}$, ‘knee’ mass $\log _{10}(M_{*}/{\rm {\rm M}_{\odot }}) = 10.07^{+0.24}_{-0.24}$ and normalisation $\log _{10}(\phi _{*}/\rm Mpc^{-3})=-2.34^{+0.32}_{-0.36}$ (H0 = 67.4 km s−1 Mpc−1) for $1/\rm V_{\rm max}$ and $\alpha =-1.44^{+0.13}_{-0.10}$, ‘knee’ mass $\log _{10}(M_{*}/{\rm {\rm M}_{\odot }}) = 10.22^{+0.10}_{-0.13}$ and normalisation $\log _{10}(\phi _{*}/\rm Mpc^{-3})=-2.52^{+0.19}_{-0.14}$ for MML. When using $1/\rm V_{\rm max}$ we find both the low-mass slope and ‘knee’ mass to be consistent within 1σ with previous studies based on single-dish surveys. The cosmological mass density of H i is found to be slightly larger than previously reported: $\Omega _{\rm HI}=5.46^{+0.94}_{-0.99} \times 10^{-4}h^{-1}_{67.4}$ from $1/\rm V_{\rm max}$ and $\Omega _{\rm HI}=6.31^{+0.31}_{-0.31} \times 10^{-4}h^{-1}_{67.4}$ from MML but consistent within the uncertainties. We find no evidence for evolution of the HIMF over the last billion years.