MIGHTEE-H I the first MeerKAT H I mass function from an untargeted interferometric survey

We present the first measurement of the H I mass function (HIMF) using data from MeerKAT, based on 276 direct detections from the MeerKAT International GigaHertz Tiered Extragalactic Exploration (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 that describes the HIMF with two different methods: 1/V_max and modified maximum likelihood (MML). We find a low-mass slope α = −1.29^+0.37_−0.26, 'knee' mass log₁₀(M_∗/M⊙) = 10.07^+0.24_−0.24 and normalization log₁₀(φ_∗/Mpc⁻³) = −2.34^+0.32_−0.36 (H₀ = 67.4 km s⁻¹ Mpc⁻¹) for 1/V_max, and α = −1.44^+0.13_−0.10, 'knee' mass log₁₀(M_∗/M⊙) = 10.22^+0.10_−0.13 and normalization log₁₀(φ_∗/Mpc⁻³) = −2.52^+0.1_−0.14 for MML. When using 1/V_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: Ω_{H I} = 5.46^+0.94_−0.99 × 10⁻⁴ h⁻¹_67.4 from 1/V_max and Ω_{H I} = 6.31^+0.31_−0.31 × 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.