The Hi Mass Function of Star-forming Galaxies at z ∼ 0.35

The neutral atomic hydrogen (Hi) mass function (HiMF) describes the distribution of the Hi content of galaxies at any epoch; its evolution provides an important probe of models of galaxy formation and evolution. Here, we report Giant Metrewave Radio Telescope Hi 21 cm spectroscopy of blue star-forming galaxies at z approximate to 0.20-0.42 in the Extended Groth Strip, which has allowed us to determine the scaling relation between the average Hi mass (M (Hi )) and the absolute B-band magnitude (M ( B )) of such galaxies at z approximate to 0.35, by stacking the Hi 21 cm emission signals of galaxy subsamples in different M ( B ) ranges. We combine this M (Hi ) - M ( B ) scaling relation (with a scatter assumed to be equal to that in the local universe) with the known B-band luminosity function of star-forming galaxies at these redshifts to determine the HiMF at z approximate to 0.35. We show that the use of the correct scatter in the M (Hi ) - M ( B ) scaling relation is critical for an accurate estimate of the HiMF. We find that the HiMF has evolved significantly from z approximate to 0.35 to z approximate to 0, i.e., over the last 4 Gyr, especially at the high-mass end. High-mass galaxies, with M (Hi ) greater than or similar to 10(10) M (circle dot), are a factor of approximate to 3.4 less prevalent at z approximate to 0.35 than at z approximate to 0. Conversely, there are more low-mass galaxies, with M (Hi ) approximate to 10(9) M (circle dot), at z approximate to 0.35 than in the local universe. While our results may be affected by cosmic variance, we find that massive star-forming galaxies have acquired a significant amount of Hi through merger events or accretion from the circumgalactic medium over the past 4 Gyr.