Neutral hydrogen (HI) gas content of galaxies at $z \approx 0.32$
  We use observations made with the Giant Metrewave Radio Telescope (GMRT) to
probe the neutral hydrogen (HI) gas content of field galaxies in the VIMOS VLT
Deep Survey (VVDS) 14h field at $z \approx 0.32$. Because the HI emission from
individual galaxies is too faint to detect at this redshift, we use an HI
spectral stacking technique using the known optical positions and redshifts of
the 165 galaxies in our sample to co-add their HI spectra and thus obtain the
average HI mass of the galaxies. Stacked HI measurements of 165 galaxies show
that 95 per cent of the neutral gas is found in blue, star-forming galaxies.
Among these galaxies, those having lower stellar mass are more gas-rich than
more massive ones. We apply a volume correction to our HI measurement to
evaluate the HI gas density at $z \approx 0.32$ as $\Omega_{HI}=(0.50\pm0.18)
\times 10^{-3}$ in units of the cosmic critical density. This value is in good
agreement with previous results at z < 0.4, suggesting no evolution in the
neutral hydrogen gas density over the last $\sim 4$ Gyr. However the $z \approx
0.32$ gas density is lower than that at $z \sim 5$ by at least a factor of two.
