Atomic Hydrogen in Star-forming Galaxies at Intermediate Redshifts

Abstract

We have used the upgraded Giant Metrewave Radio Telescope to carry out a deep (117 on-source hours) L -band observation of the Extended Groth Strip, to measure the average neutral hydrogen (H i ) mass and median star formation rate (SFR) of star-forming galaxies, as well as the cosmic H i mass density, at 0.2 <  z  < 0.4. This was done by stacking the H i 21 cm emission and the rest-frame 1.4 GHz radio continuum from 445 blue star-forming galaxies with M B  ≤ −17 at z mean  ≈ 0.34. The stacked H i 21 cm emission signal is detected at ≈7 σ significance, implying an average H i mass of . We also stacked the rest-frame 1.4 GHz radio continuum emission of the same galaxies to obtain a median SFR of (0.54 ± 0.06) M ⊙ yr −1 ; this implies an atomic gas depletion timescale of Δ t H i  = (≈9) Gyr, consistent with values in star-forming galaxies in the local universe. This indicates that the star formation efficiency does not change significantly over the redshift range 0–0.4. We used the detection of the stacked H i 21 cm emission signal to infer the normalized cosmic H i mass density ( ρ H i / ρ c,0 ) in star-forming galaxies at z  ≈ 0.34. Assuming the local relation between H i mass and absolute B -magnitude, we obtain ρ H i / ρ c,0  = (4.81 ± 0.75) × 10 −4 , implying no significant evolution in ρ H i / ρ c,0 from z  ≈ 0.4 to the present epoch.