Atomic Gas Scaling Relations of Star-forming Galaxies at z ≈ 1

Abstract

We use the Giant Metrewave Radio Telescope Cold-H i AT z ≈ 1 (CAT z 1) survey, a 510 hr H i 21 cm emission survey of galaxies at z = 0.74–1.45, to report the first measurements of atomic hydrogen (H i ) scaling relations at z ≈ 1. We divide our sample of 11,419 blue star-forming galaxies at z ≈ 1 into three stellar-mass ( M * ) subsamples and obtain detections (at ≥4 σ significance) of the stacked H i 21 cm emission signal from galaxies in all three subsamples. We fit a power-law relation to the measurements of the average H i mass ( M HI ) in the three stellar-mass subsamples to find that the slope of the M HI – M * relation at z ≈ 1 is consistent with that at z ≈ 0. However, we find that the M HI – M * relation has shifted downwards from z ≈ 1 to z ≈ 0, by a factor of 3.54 ± 0.48. Further, we find that the H i depletion timescales ( t dep,HI ) of galaxies in the three stellar-mass subsamples are systematically lower than those at z ≈ 0, by factors of ≈2–4. We divide the sample galaxies into three specific star formation rate (sSFR) subsamples, again obtaining ≥4 σ detections of the stacked H i 21 cm emission signal in all three subsamples. We find that the relation between the ratio of H i mass to stellar mass and the sSFR evolves between z ≈ 1 and z ≈ 0. Unlike the efficiency of conversion of molecular gas to stars, which does not evolve significantly with redshift, we find that the efficiency with which H i is converted to stars is much higher for star-forming galaxies at z ≈ 1 than those at z ≈ 0.