The gas mass of star-forming galaxies at z ≈ 1.3

We report a Giant Metrewave Radio Telescope search for H i 21 cm emission from a large sample of massive star-forming galaxies at z ≈ 1.18–1.34, lying in sub-fields of the DEEP2 Redshift Survey. The search was carried out by co-adding ("stacking") the H i 21 cm emission spectra of 857 galaxies, after shifting each galaxy's H i 21 cm spectrum to its rest frame. We obtain the 3σ upper limit S_{H i} < 2.5 μJy on the average H i 21 cm flux density of the 857 galaxies, at a velocity resolution of ≈315 km s⁻¹. This yields the 3σ constraint $M_{HI}<2.1\times {10}^{10}\times {\left[\Delta V/315{\text{km s}}^{-1}\right]}^{1/2}{M}_{\odot }$ on the average H i mass of the 857 stacked galaxies, the first direct constraint on the atomic gas mass of galaxies at z > 1. The implied limit on the average atomic gas mass fraction (relative to stars) is M_GAS/M_* < 0.5, comparable to the cold molecular gas mass fraction in similar star-forming galaxies at these redshifts. We find that the cosmological mass density of neutral atomic gas in massive star-forming galaxies at z ≈ 1.3 is Ω_GAS < 3.7 × 10⁻⁴, significantly lower than Ω_GAS estimates in both galaxies in the local universe and damped Lyα absorbers at z ≥ 2.2. Massive blue star-forming galaxies thus do not appear to dominate the neutral atomic gas content of the universe at z ≈ 1.3.