Paper detail

Semi-empirical constraints on the HI mass function of star-forming galaxies and $Ω_{\rm HI}$ at $z\sim 0.37$ from interferometric surveys

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 $z\sim 0.37$ by combining literature results on the $M_\star$ function from optical surveys with recent findings on the $M_{\rm HI}-M_\star$ 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 $M_\star$ samples directly from the publicly-available results underlying the analysis of the COSMOS2020 galaxy photometric sample. Afterwards, we convert $M_\star$ into $M_{\rm HI}$ 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 $Ω_{\rm HI}$ by integrating the models for the HIMF built from the posteriors samples of the Schechter parameters. We find a deviation of the HIMF at $z\sim 0.37$ from the results at $z\sim 0$ from the ALFALFA survey and at $z\sim 1$ from uGMRT data. Our results for $Ω_{\rm HI}$ are in broad agreement with other literature results, and follow the overall trend on $Ω_{\rm HI}$ as a function of redshift. The derived value $Ω_{\rm HI}=\left(7.02^{+0.59}_{-0.52}\right)\times10^{-4}$ at $z\sim 0.37$ from the combined analysis deviates at $\sim 2.9σ$ from the ALFALFA result at $z\sim 0$. Our findings about the HIMF and $Ω_{\rm HI}$ differ from previous literature results at $z\sim0$ and $z\sim1$, 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.