Atomic Hydrogen Scaling Relations at z ≈ 0.35

Abstract

The atomic hydrogen (H i ) properties of star-forming galaxies in the local universe are known to correlate with other galaxy properties via the “H  i 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 H i scaling relations at cosmological distances. Using data from a deep Giant Metrewave Radio Telescope H i 21 cm survey of the Extended Groth Strip, and the technique of spectral-line stacking, we determine the scaling relation between the H i  mass and the stellar mass for star-forming galaxies at z ≈ 0.35. We use this measurement, along with the main-sequence relation in galaxies, to infer the dependence of the H  i depletion timescale of these galaxies on their stellar mass. We find that massive star-forming galaxies at z ≈ 0.35, with stellar mass M * ≳ 10 9.5 M ⊙ , are H  i -poor compared to local star-forming galaxies of a similar stellar mass. However, their characteristic H i depletion time is lower by a factor of ≈5 than that of their local analogs, indicating a higher star formation efficiency at intermediate redshifts (similar to that at z ≈ 1). While our results are based on a relatively small cosmic volume and could thus be affected by cosmic variance, the short characteristic H  i depletion timescales (≲3 Gyr) of massive star-forming galaxies at z ≈ 0.35 indicate that they must have acquired a significant amount of neutral gas through accretion from the circumgalactic medium over the past 4 Gyr, to avoid quenching of their star formation activity.