Constraining the z about 1 neutral hydrogen (HI) distribution

We constrain the z about 1 HI distribution by jointly modeling two independent, existing observations of the 21-cm signal, the HI density parameter HI measured using uGMRT by stacking the 21-cm emission from blue, star-forming galaxies, and the 21-cm autocorrelation power spectrum (PS) measured using CHIME. We assign HI to the dark matter halos in a cosmological simulation using an HI mass-halo mass (HIHM) relation with three free parameters whose values we estimate by performing a joint Bayesian inference comparing the simulated HI and 21-cm PS with the measurements. We use the inferred HIHM posterior to simulate the HI distribution and predict the z about 1 HI mass function (HIMF). We find that the HIMF remains nearly constant at low HI masses (3.6 times 10 9 M), and it declines rapidly for larger HI masses. Around about 90 percent of the total HI gas is contained in the mass range M HI in [2 times 10 9,, 4 times 10 11], M. Our estimates predict a larger abundance of high mass HI galaxies than predicted by earlier observations and hydrodynamical simulations. We expect these results to be useful in understanding galaxy evolution and star formation.