Observations of Chemically Enriched QSO Absorbers near z ~ 2.3 Galaxies: Galaxy-Formation Feedback Signatures in the IGM

摘要

We present a study of galaxies and intergalactic gas toward the z=2.73 quasarHS1700+6416, to explore the effects of galaxy formation feedback on the IGM.Our observations and ionization simulations indicate that the volume within100-200 h_71^{-1} physical kpc of high-redshift galaxies contains very small,dense, and metal-rich absorption-line regions. These systems often containshock-heated gas seen in OVI, and may exhibit [Si/C] abundance enhancementssuggestive of Type II supernova enrichment. We argue that the absorbersresemble thin sheets or bubbles, whose physical properties can be explainedwith a simple model of radiatively efficient shocks propegating through theIGM. Their high metallicities suggest that these shocks are being expelledfrom--rather than falling into--star forming galaxies. There is a dropoff inthe IGM gas density at galaxy impact parameters beyond ~300 physical kpc thatmay trace boundaries of gas structures where the galaxies reside. The localheavy-element enhancement covers 100-200 kpc; beyond this the observedabundances blend into the general IGM. Supernova-driven winds or dynamicalstripping of interstellar gas appears to affect the IGM near massive galaxies,even at R>~100 kpc. However, these feedback systems represent only a fewpercent of the Lya forest mass at z~2.5. Their mass could be larger if the morenumerous metal-poor CIV systems at >~200 kpc are tepid remnants of verypowerful winds. Based on present observations it is not clear that thisscenario is to be favored over one involving pre-enrichment by smaller galaxiesat z>~6.