  As part of a program to study the relationship between QSO Lyman alpha clouds
and galaxies at low redshifts, we have obtained a high signal-to-noise far UV
spectrum of H 1821+643 [z(em) = 0.297] with the G140L grating of the GHRS. The
spectrum, which has a resolution of FWHM = 150 km/s and S/N ~ 100:1, is
adequate for detection of weak Ly alpha clouds with equivalent width as low as
50 mA (4sigma) with complete spectral coverage from z_(abs) = 0.03 to z(abs) =
0.26. In this paper we present some preliminary results of this study including
the following. (1) The absorption profiles of three out of the four strongest
extragalactic Ly alpha lines show complex component structure with a main
strong component and several weaker outlying components spanning a full
velocity range of ~1000-1500 km/s. The two-point correlation function does not
show any evidence of Ly alpha cloud clustering but suffers from small number
statistics. (2) Extragalactic O VI is clearly detected in the intervening
absorption system at z_(abs) = 0.225. Two galaxies at z = 0.2256 and z = 0.2263
are close to the sight line (the closer galaxy is at a projected distance of
~90 kpc), so this O VI absorption could be due to the intracluster medium of a
group of galaxies.

Astrophysics