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

We present the first measurement of the HI mass function (HIMF) using data from MeerKAT, based on 276 direct detections from the MeerKAT International Gig aHertz Tiered Extrag alactic Exploration (MIGHTEE) Surv e y Early Science data co v ering a period of approximately a billion years (0 <= z <= 0.084). This is the first HIMF measured using interferometric data o v er 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 alpha = -1.29(-0.26)(+0.37), knee' mass log(10)(M-*/M-circle dot) = 10.07(-0.24)(+0.24) and normalization log10(phi(*)/Mpc(-3)) = -2.34(-0.36)(+0.32) (H-0 = 67.4 km s(-1) Mpc(-1)) for 1 = 1/V-max , and alpha = -1.44(-0.10)(+0.13), knee' mass log(10)(M-*/M-circle dot) = 10.22(-0.13)(+0.10) and normalization log10(phi(*)/Mpc(-3)) = -2.52(-0.14)(+0.19) for MML. When using 1/V-max we find both the low-mass slope and knee' mass to be consistent within 1 sigma with previous studies based on single-dish surv e ys. The cosmological mass density of HI is found to be slightly larger than previously reported: Omega(HI) = 5.46(-0.99)(+0.94) x 10(-4) h(67.4)(-1) from 1/V-max and Omega(HI) = 6.31(-0.31)(+0.31) x 10(-4) h(67.4)(-1) from MML but consistent within the uncertainties. We find no evidence for evolution of the HIMF o v er the last billion years.