We report observations from the Hubble Space Telescope ( HST ) and the VLA on the galactic environment , metallicity , and D/H in strong low-redshift Ly \alpha absorption systems toward the bright BL Lac object PKS 2155-304 .
These studies are intended to clarify the origin and chemical evolution of gas at large distances from galaxies .
With GHRS/G160M data at \sim 20 km s ^ { -1 } resolution , we detect a total of 14 Ly \alpha absorbers , six of them clustered between cz = 16 , 100 and 18,500 km s ^ { -1 } .
Although ORFEUS studies claimed Lyman continuum ( Lyc ) absorption at z \approx 0.056 with N ( H I ) = ( 2 - 5 ) \times 10 ^ { 16 } cm ^ { -2 } , the Ly \alpha data suggest a range , N ( H I ) = ( 3 - 10 ) \times 10 ^ { 14 } cm ^ { -2 } .
Even higher columns , needed for consistency with the ORFEUS Lyc results , are possible if the Ly \alpha line core at 17 , 000 \pm 50 km s ^ { -1 } contains narrow H I components .
We identify the Ly \alpha cluster with a group of five H I galaxies offset by ( 400 - 800 ) h _ { 75 } ^ { -1 } kpc from the sightline .
The two strongest absorption features cover the same velocity range as the H I emission in the two galaxies closest to the line of sight .
If the Ly \alpha is associated with these galaxies , they must have huge halos ( 400 - 500 h _ { 75 } ^ { -1 } kpc ) of highly turbulent , mostly ionized gas .
The Ly \alpha absorption could also arise from an extended sheet of intragroup gas , or from smaller primordial clouds and halos of dwarf galaxies .

We see no absorption from Si III \lambda 1206 , C IV \lambda 1548 , or deuterium Ly \alpha at the expected positions of the strongest Ly \alpha absorbers .
Photoionization models yield ( 4 \sigma ) limits of ( Si/H ) \leq 0.003 { ( Si / H ) } _ { \odot } , ( C/H ) \leq 0.005 { ( C / H ) } _ { \odot } , and ( D/H ) \leq 2.8 \times 10 ^ { -4 } if N ( H I ) has the ORFEUS value of 2 \times 10 ^ { 16 } cm ^ { -2 } .
The limits increase to 0.023 solar metallicity and D/H \leq 2.8 \times 10 ^ { -3 } if N ( H I ) is only 2 \times 10 ^ { 15 } cm ^ { -2 } .
These limits can be improved with further studies by HST/STIS and measurements of the Lyc and higher Lyman series absorption by FUSE .
However , the current data suggest that the intergalactic gas in this group has not been enriched to the levels suggested by X-ray studies of intracluster gas .
Because of their low metallicity and large distance from galaxies , these absorbers could be primordial gas clouds .