The HI mass function is a crucial tool to understand the evolution of the HI content in galaxies over cosmic times. We aim to derive semi-empirical constraints at z 0. 37 by combining literature results on the M_ function from optical surveys with recent findings on the M ₇₈-M_ scaling relation derived via spectral stacking analysis applied to 21-cm line interferometric data from the MIGHTEE and CHILES surveys, conducted with the MeerKAT and VLA radio telescopes, respectively. We draw synthetic M_ samples directly from the publicly-available results underlying the analysis of the COSMOS2020 galaxy photometric sample. Afterwards, we convert M_ into M ₇₈ using analytical fitting functions to the data points from HI stacking. We then fit a Schechter function to the median HIMF from all the samples via MCMC. We finally derive the posterior distribution for Ω ₇₈ by integrating the models for the HIMF built from the posteriors samples of the Schechter parameters. We find a deviation of the HIMF at z 0. 37 from the results at z 0 from the ALFALFA survey and at z 1 from uGMRT data. Our results for Ω ₇₈ are in broad agreement with other literature results, and follow the overall trend on Ω ₇₈ as a function of redshift. The derived value Ω ₇₈= (7. 02^+0. 59-₀. ₅₂) 10^-4 at z 0. 37 from the combined analysis deviates at 2. 9σ from the ALFALFA result at z 0. Our findings about the HIMF and Ω ₇₈ differ from previous literature results at z0 and z1, although we are unable to confirm at this stage whether these differences are due to cosmic evolution consistent with a smooth transition of the HI content of galaxies over the last 8 Gyr or due to selection biases and systematics.
Sinigaglia et al. (Thu,) studied this question.