We used observations from the Giant Metrewave Radio Telescope to measure the atomic hydrogen gas content of 324 galaxies around the galaxy cluster Abell 370 at a redshift of z = 0.37 ( a look-back time of \sim 4 billion years ) .
The H i 21-cm emission from these galaxies was measured by coadding their signals using precise optical redshifts obtained with the Anglo-Australian Telescope .
The average H i mass measured for all 324 galaxies is ( 6.6 \pm 3.5 ) \times 10 ^ { 9 } M _ { \odot } , while the average H i mass measured for the 105 optically blue galaxies is ( 19.0 \pm 6.5 ) \times 10 ^ { 9 } M _ { \odot } .
The significant quantities of gas found around Abell 370 , suggest that there has been substantial evolution in the gas content of galaxy clusters since redshift z = 0.37 .
The total amount of atomic hydrogen gas found around Abell 370 is up to \sim 8 times more than that seen around the Coma cluster , a nearby galaxy cluster of similar size .
Despite this higher gas content , Abell 370 shows the same trend as nearby clusters , that galaxies close to the cluster core have lower H i gas content than galaxies further away where the galaxy density is lower .
The optically blue galaxies contain the majority of the H i gas surrounding the cluster .
However , there is evidence that the optically red galaxies contain appreciable quantities of H i gas within their central regions .
The Abell 370 galaxies have H i mass to optical light ratios similar to local galaxy samples and have the same correlation between their star formation rate and H i mass as found in nearby galaxies .
The average star formation rate derived from [ OII ] emission and from de-redshifted 1.4 GHz radio continuum for the Abell 370 galaxies also follows the correlation found in the local universe .
The large amounts of H i gas found around the cluster can easily be consumed entirely by the observed star formation rate in the galaxies over the \sim 4 billion years ( from z = 0.37 ) to the present day .
Abell 370 appears set to evolve into a gas poor system similar to galaxy clusters observed in the local universe .