THE GAS MASS OF STAR-FORMING GALAXIES AT z ≈ 1.3

Abstract

ABSTRACT 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 H I < 2.1 × 10 10 × [ Δ V / 315 km s − 1 ] 1 / 2 M ⊙ ?> 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 ΩGAS < 3.7 × 10−4, significantly lower than ΩGAS 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.