The Giant Metrewave Radio Telescope Cold-Hi AT z ≈ 1 Survey

Abstract We describe the design, data analysis, and basic results of the Giant Metrewave Radio Telescope Cold-Hi AT z ≈ 1 (GMRT-CATz1) survey, a 510 hr upgraded GMRT Hi 21 cm emission survey of galaxies at z = 0.74−1.45 in the DEEP2 survey fields. The GMRT-CAT z1 survey is aimed at characterizing Hi in galaxies during and just after the epoch of peak star formation activity in the universe, a key epoch in galaxy evolution. We obtained high-quality Hi 21 cm spectra for 11,419 blue star-forming galaxies at z = 0.74−1.45, in seven pointings on the DEEP2 subfields. We detect the stacked Hi 21 cm emission signal of the 11,419 star-forming galaxies, which have an average stellar mass of M * ≈ 1010 M ⊙, at 7.1σ statistical significance, obtaining an average Hi mass of 〈M H i 〉 = (13.7 ± 1.9) × 109 M ⊙. This is significantly higher than the average Hi mass of 〈M H i 〉 = (3.96 ± 0.17) × 109 M ⊙ in star-forming galaxies at z ≈ 0 with an identical stellar-mass distribution. We stack the rest-frame 1.4 GHz continuum emission of our 11,419 galaxies to infer an average star formation rate (SFR) of 8.07 ± 0.82 M ⊙ yr−1. Combining our average Hi mass and average SFR estimates yields an Hi depletion timescale of 1.70 ± 0.29 Gyr, for star-forming galaxies at z ≈ 1, ≈3 times lower than that of local galaxies. We thus find that, although main-sequence galaxies at z ≈ 1 have a high Hi mass, their short Hi depletion timescale is likely to cause quenching of their star formation activity in the absence of rapid gas accretion from the circumgalactic medium.