Atomic hydrogen scaling relations at $z \approx 0.35$

The atomic hydrogen (HI) properties of star-forming galaxies in the local Universe are known to correlate with other galaxy properties via the ``HI scaling relations''. The redshift evolution of these relations serves as an important constraint on models of galaxy evolution. However, until recently, there were no estimates of the HI scaling relations at cosmological distances. Using data from a deep Giant Metrewave Radio Telescope HI 21 cm survey of the Extended Groth Strip, and the technique of spectral line stacking, we determine the scaling relation between the HI mass and the stellar mass for star-forming galaxies at $z\approx0.35$. We use this measurement, along with the main-sequence relation in galaxies, to infer the dependence of the HI depletion timescale of these galaxies on their stellar mass. We find that massive star-forming galaxies at $z\approx0.35$, with stellar mass $\rm M_* \gtrsim10^{9.5}\:M_{\odot}$, are HI-poor compared to local star-forming galaxies of a similar stellar mass. However, their characteristic HI depletion time is lower by a factor of $\approx 5$ than that of their local analogues, indicating a higher star-formation efficiency at intermediate redshifts (similar to that at $z \approx 1$). While our results are based on a relatively small cosmic volume and could thus be affected by cosmic variance, the short characteristic HI depletion timescales ($\lesssim 3$ Gyr) of massive star-forming galaxies at $z \approx 0.35$ indicate that they must have acquired a significant amount of neutral gas through accretion from the circumgalactic medium over the past four Gyr, to avoid quenching of their star-formation activity.