Conclusions

The QSO absorption-line data on the 2142-4420 cluster are provocative. If taken at face value, they suggest that this high redshift cluster, and perhaps all of them, are surrounded by Mpc structures of neutral hydrogen, of total mass

. This gas would be gathered into a series of > 20kpc clumps, each of which is made up of hundreds of small (< 500 pc), dense (

) clouds. These clouds may merge to form cluster galaxies, collapse to form globular clusters, or perhaps dissolve into X-ray intra-cluster medium by redshift zero.

Many more observations of neutral gas around high redshift clusters will be needed to verify this picture.

© Copyright Astronomical Society of Australia 1997