OBSERVATIONS OF CHEMICALLY ENRICHED QSO ABSORBERS NEAR z ～ 2.3 GALAXIES: GALAXY FORMATION FEEDBACK SIGNATURES IN THE INTERGALACTIC MEDIUM

摘要

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_(71)~(-1) physical kpc of high-redshift galaxies is populated by very small (ΔL approx < 1 kpc), dense (ρ/ρ ～ 1000), and metal-rich (Z approx > 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 approx > 300 physical kpc (approx > 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_(71)~(-1) kpc 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 approx > 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 approx > 200 h_(71)~(-1) kpc 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 approx > 6.