Atomic Gas Scaling Relations of Star-forming Galaxies at $z \approx 1$

TL;DR

This study measures atomic hydrogen scaling relations in star-forming galaxies at redshift ~1, revealing a downward shift in HI mass relative to stellar mass and higher HI-to-star conversion efficiency compared to local galaxies.

Contribution

First measurement of HI scaling relations at z~1 using GMRT, showing evolution in HI content and star formation efficiency over cosmic time.

Findings

HI mass-stellar mass relation slope remains consistent from z~1 to z~0

HI mass relative to stellar mass decreases by a factor of ~3.5 from z~1 to z~0

HI-to-stellar mass conversion efficiency is higher at z~1 than at z~0

Abstract

We use the Giant Metrewave Radio Telescope (GMRT) Cold-HI AT $z\approx1$ (CAT$z1$) survey, a 510 hr HI 21cm emission survey of galaxies at $z=0.74-1.45$, to report the first measurements of atomic hydrogen (HI) scaling relations at $z\approx1$. We divide our sample of 11,419 blue star-forming galaxies at $z\approx1$ into three stellar mass ($M_*$) subsamples and obtain detections (at $\geq 4\sigma$ significance) of the stacked HI 21cm 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 $z\approx1$ is consistent with that at $z\approx0$. However, we find that the $M_{HI}-M_{*}$ relation has shifted downwards from $z\approx1$ to $z\approx0$, by a factor of $3.54\pm0.48$. 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 $z\approx0$, by factors of $\approx2-4$. We divide the sample galaxies into three specific star-formation rate (sSFR) subsamples, again obtaining $\geq 4\sigma$ detections of the stacked HI 21cm 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 $z\approx1$ and $z\approx0$. 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 $z\approx1$ than those at $z\approx0$.