2006ApJ...637..648S

We present a comparative study of galaxies and intergalactic gas toward the z=2.73 quasar HS 1700+6416, to explore the effects of galaxy formation feedback on the IGM. Our observations and ionization simulations indicate that the volume within 100-200 h^–1₇₁physical kpc of high-redshift galaxies is populated by very small (ΔL≲1 kpc), dense (ρ/ρ{d1}∼1000), and metal-rich (Z≳(1)/(10)-(1)/(3) Z_☉) absorption-line regions. These systems often contain shock-heated gas seen in O VI and may exhibit [Si/C] abundance enhancements suggestive of preferential enrichment by Type II supernovae. We argue that the absorber geometries resemble thin sheets or bubbles and that their unusual physical properties can be explained using a simple model of radiatively efficient shocks plowing through moderately overdense intergalactic filaments. The high metallicities suggest that these shocks are being expelled from, rather than falling into, star-forming galaxies. There is a drop-off in the intergalactic gas density at galaxy impact parameters of ≳300 physical kpc (≳1 comoving Mpc) that may represent boundaries of the gas structures where galaxies reside. The heavy-element enhancement near galaxies covers smaller distances: at galactocentric radii between 100 and 200 h^–1₇₁kpc the observed abundances blend into the general metallicity field of the IGM. Our results suggest that either supernova-driven winds or dynamical stripping of interstellar gas alters the IGM near massive galaxies, even at R≳100 kpc. However, only a few percent of the total mass in the Lyα forest is encompassed by this active feedback at z∼2.5. The effects could be more widespread if the more numerous metal-poor C IV systems at impact parameters ≳200 h^–1₇₁kpc are the tepid remnants of very powerful late-time winds. However, based on present observations it is not clear that this scenario is to be favored over one involving preenrichment by smaller galaxies at z≳6.