Neutral atomic hydrogen (HI) gas evolution in field galaxies at z ~ 0.1 and 0.2

TL;DR

This study measures the average neutral hydrogen gas content in field galaxies at z ~ 0.1 and 0.2 using stacking of 21-cm emission lines, finding no significant evolution in cosmic HI density over the last 2.4 billion years.

Contribution

It provides new measurements of cosmic HI density at intermediate redshifts, bridging the gap between high-redshift Lyman-alpha and local 21-cm surveys, confirming no evolution in HI content in recent cosmic history.

Findings

Measured {1}HI density at z ~ 0.1 and 0.2 with consistent values.

Found no significant evolution of cosmic HI density over 2.4 Gyr.

Results align with previous local universe measurements.

Abstract

We measure the neutral atomic hydrogen (HI) gas content of field galaxies at intermediate redshifts of z ~ 0.1 and z ~ 0.2 using hydrogen 21-cm emission lines observed with the Westerbork Synthesis Radio Telescope (WSRT). In order to make high signal-to-noise ratio detections, an HI signal stacking technique is applied: HI emission spectra from multiple galaxies, optically selected by the CNOC2 redshift survey project, are co-added to measure the average HI mass of galaxies in the two redshift bins. We calculate the cosmic HI gas densities ({\Omega}_{HI}) at the two redshift regimes and compare those with measurements at other redshifts to investigate the global evolution of the HI gas density over cosmic time. From a total of 59 galaxies at z ~ 0.1 we find {\Omega}_{HI} = (0.33 $\pm$ 0.05) ~ $\times$ 10$^{-3}$, and at z ~ 0.2 we find {\Omega}_{HI} = (0.34 $\pm$ 0.09) ~ $\times$ 10$^{-3}$, based on 96 galaxies. These measurements help bridge the gap between high-z damped Lyman-$\alpha$ observations and blind 21-cm surveys at $z=$ 0. We find that our measurements of {\Omega}_{HI} at z ~ 0.1 and 0.2 are consistent with the HI gas density at z ~ 0 and that all measurements of {\Omega}_{HI} from 21-cm emission observations at $z \la$ ~ 0.2 are in agreement with no evolution of the HI gas content in galaxies during the last 2.4 Gyr.