Neutral atomic hydrogen (H i) gas evolution in field galaxies at z ∼ 0.1 and ∼0.2

Abstract

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