Clues to the origin of metals in the Ly α forest

We analyze the z = 2 Lyα and C IV forest along two adjacent lines-of-sight at high S/N and spectral resolution to assess the question of the origin of metals in the intergalactic medium. We find that the gas containing detectable amounts of metals (as seen in absorption by C IV) is less quiescent on scales of a few kpc than the gas without metals. Although it is difficult to discriminate unequivocally between possible sources of enrichment and the extent to which each contributes to line-of-sight differences, those suggest that the metal-enriched systems are bound to galaxies (i.e., they do not arise in the IGM nor in galactic winds). 1.1 Introduction The high-z IGM is inhomogeneously distributed on large-scales in voids and filaments ; it contains a large fraction of baryons (Rauch, Haehnelt & Steinmetz 1997) and is highly ionized and warm (∼ 10 4 K). Despite a low neutral fraction, a large range of densities —from slightly underdense gas up to the denser environment of collapsed objects— can be probed via H I absorption of photons from background QSOs. This is called the Lyα forest. The optical depth of the H I, τ Lyα , maps overdensities in the low density regime. The higher the H I column density, the stronger and kinematically more complex the system.