We present high-resolution ultraviolet spectra of absorption-line systems toward the low - z QSO HS 0624+6907 ( z _ { QSO } = 0.3700 ) .
Coupled with ground-based imaging and spectroscopic galaxy redshifts , we find evidence that many of these absorbers do not arise in galaxy halos but rather are truly integalactic gas clouds distributed within large-scale structures , and moreover , the gas is cool ( T < 10 ^ { 5 } K ) and has relatively high metallicity ( Z = 0.9 Z _ { \odot } ) . HST Space Telescope Imaging Spectrograph ( STIS ) data reveal a dramatic cluster of 13 H I Ly \alpha lines within a 1000 km s ^ { -1 } interval at z _ { abs } = 0.0635 .
We find 10 galaxies at this redshift with impact parameters ranging from \rho = 135 h _ { 70 } ^ { -1 } kpc to 1.37 h _ { 70 } ^ { -1 } Mpc .
The velocities and velocity spread of the Ly \alpha lines in this complex are unlikely to arise in the individual halos of the nearby galaxies ; instead , we attribute the absorption to intragroup medium gas , possibly from a large-scale filament viewed along its long axis .
Contrary to theoretical expectations , this gas is not the shock-heated warm-hot intergalactic medium ( WHIM ) ; the width of the Ly \alpha lines all indicate a gas temperature T \ll 10 ^ { 5 } K , and metal lines detected in the Ly \alpha complex also favor photoionised , cool gas .
No O VI absorption lines are evident , which is consistent with photoionisation models .
Remarkably , the metallicity is near-solar , [ M/H ] = -0.05 \pm 0.4 ( 2 \sigma uncertainty ) , yet the nearest galaxy which might pollute the IGM is at least 135 h _ { 70 } ^ { -1 } kpc away .
Tidal stripping from nearby galaxies appears to be the most likely origin of this highly enriched , cool gas .
More than six Abell galaxy clusters are found within 4 ^ { \circ } of the sight line suggesting that the QSO line of sight passes near a node in the cosmic web .
At z \approx 0.077 , we find absorption systems as well as galaxies at the redshift of the nearby clusters Abell 564 and Abell 559 .
We conclude that the sight line pierces a filament of gas and galaxies feeding into these clusters .
The absorber at z _ { abs } = 0.07573 associated with Abell 564/559 also has a high metallicity with [ C/H ] > -0.6 , but again the closest galaxy is relatively far from the sight line ( \rho = 293 h _ { 70 } ^ { -1 } kpc ) .
The Doppler parameters and H I column densities of the Ly \alpha lines observed along the entire sight line are consistent with those measured toward other low - z QSOs , including a number of broad ( b > 40 km s ^ { -1 } ) Ly \alpha lines .