The HI Mass Function of Star-forming Galaxies at z1

We present the first estimate of the HI mass function (HIMF) of star-forming galaxies at z1, obtained by combining our measurement of the scaling relation between HI mass (M₇₈) and B-band luminosity (MB) of star-forming galaxies with literature estimates of the B-band luminosity function at z1. We determined the M₇₈-MB relation by using the GMRT-CATz1 survey of the DEEP2 fields to measure the average HI mass of blue galaxies at z=0. 74-1. 45 in three separate MB subsamples. This was done by separately stacking the HI 21 cm emission signals of the galaxies in each subsample to detect, at (3. 5-4. 4) significance, the average HI 21 cm emission of each subsample. We find that the M₇₈-MB relation at z1 is consistent with that at z0. We combine our estimate of the M₇₈-MB relation at z1 with the B-band luminosity function at z1 to determine the HIMF at z1. We find that the number density of galaxies with M₇₈>10^10 M_ (higher than the knee of the local HIMF) at z1 is a factor of 4-5 higher than that at z0, for a wide range of assumed scatters in the M₇₈-MB relation. We rule out the hypothesis that the number density of galaxies with M₇₈>10^10 M_ remains unchanged between z 1 and z0 at 99. 7\% confidence. This is the first statistically significant evidence for evolution in the HIMF of galaxies from the epoch of cosmic noon.