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
(Ømega_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 Ømega_HI
= (0.33 $\pm$ 0.05) ~ $\times$ 10$^-3$, and at z ~ 0.2 we find Ømega_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 Ømega_HI at z ~ 0.1 and 0.2 are consistent with the HI gas density at z
~ 0 and that all measurements of Ømega_HI from 21-cm emission observations
at $z ła$ ~ 0.2 are in agreement with no evolution of the HI gas content in
galaxies during the last 2.4 Gyr.
Users
Please
log in to take part in the discussion (add own reviews or comments).