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

We use the Giant Metrewave Radio Telescope Cold-Hi AT z approximate to 1 (CATz1) survey, a 510 hr Hi 21 cm emission survey of galaxies at z = 0.74-1.45, to report the first measurements of atomic hydrogen (Hi) scaling relations at z approximate to 1. We divide our sample of 11,419 blue star-forming galaxies at z approximate to 1 into three stellar-mass (M (*)) subsamples and obtain detections (at >= 4 sigma significance) of the stacked Hi 21 cm emission signal from galaxies in all three subsamples. We fit a power-law relation to the measurements of the average Hi mass (M (HI)) in the three stellar-mass subsamples to find that the slope of the M (HI)-M (*) relation at z approximate to 1 is consistent with that at z approximate to 0. However, we find that the M (HI)-M (*) relation has shifted downwards from z approximate to 1 to z approximate to 0, by a factor of 3.54 +/- 0.48. Further, we find that the Hi depletion timescales (t (dep,HI)) of galaxies in the three stellar-mass subsamples are systematically lower than those at z approximate to 0, by factors of approximate to 2-4. We divide the sample galaxies into three specific star formation rate (sSFR) subsamples, again obtaining >= 4 sigma detections of the stacked Hi 21 cm emission signal in all three subsamples. We find that the relation between the ratio of Hi mass to stellar mass and the sSFR evolves between z approximate to 1 and z approximate to 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 Hi is converted to stars is much higher for star-forming galaxies at z approximate to 1 than those at z approximate to 0.

Automated summary

In this study, the authors conducted a survey of galaxies at z approximate to 1 using the Giant Metrewave Radio Telescope, and measured the scaling relations of atomic hydrogen (Hi). The results show that the relation between Hi mass and stellar mass has shifted downwards from z approximate to 1 to z approximate to 0, and the Hi depletion timescales are lower at z approximate to 1. Furthermore, the efficiency with which Hi is converted to stars is higher for star-forming galaxies at z approximate to 1 compared to z approximate to 0.