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On the Gas Surrounding High Redshift Galaxy Clusters1

On the Gas Surrounding High Redshift Galaxy Clusters1

Paul J Francis , Greg M. Wilson , Bruce E. Woodgate, PASA, 18 (1), in press.
Next Section: Introduction
Contents Page: Volume 18, Number 1

On the Gas Surrounding High Redshift Galaxy Clusters1

Paul J Francis 2,3
Greg M. Wilson 2
Bruce E. Woodgate 4

2 Research School of Astronomy and Astrophysics, Australian National University, Canberra ACT 0200: pfrancis, gmw@mso.anu.edu.au

3 Joint appointment with the Department of Physics, Faculty of Science

4 NASA Goddard Space-Flight Center, Code 681, Greenbelt, MD 20771, USA: woodgate@s2.gsfc.nasa.gov

Abstract:

Francis & Hewett (1993) identified two 10-Mpc scale regions of the high redshift universe that were seemingly very overdense in neutral hydrogen. Subsequent observations showed that at least one of these gas-rich regions enveloped a cluster of galaxies at redshift 2.38. We present improved observations of the three background QSOs with sightlines passing within a few Mpc of this cluster of galaxies. All three QSOs show strong neutral hydrogen absorption at the cluster redshift, suggesting that this cluster (and perhaps all high redshift clusters) may be surrounded by a $\sim 5$ Mpc scale region containing

$\sim 10^{12} M_{\odot }$ of neutral gas.

If most high redshift clusters are surrounded by such regions, we show that the gas must be in the form of many small (< 1 kpc), dense (

$> 0.03 {\rm\ cm}^{-3}$) clouds, each of mass

$< 10^6 M_{\odot }$. These clouds are themselves probably gathered into > 20 kpc sized clumps, which may be galaxy halos or protogalaxies.

If this gas exists, it will be partially photoionised by the UV background. We predict the diffuse Ly$\alpha $ flux from this photoionisation, and place observational limits on its intensity.

Keywords: galaxies: clusters: individual (2142-4420) -- galaxies: distances and redshifts -- quasars: absorption lines



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