Absorbers in the suburbs: HST views the local Ly[alpha] forest

We describe recent discoveries of low column density (N_HI = 10^12.5-16.0 cm^-2) H I Lyα absorbers made with the Hubble Space Telescope (HST) which have allowed us a first look at gas in local intergalactic space; i.e., between us and the "Great Wall". These absorbing clouds account for 29 ± 4% of all baryons at z=0 and are, in general, only loosely related to individual galaxies. Owing to the proximity of these absorbers to the Earth, the 187 absorbers in our combined GHRS + STIS sample provide our best view of the relationship between Lyα absorbers and galaxies, voids, and supercluster filaments. While only a few of the very strongest absorbers in our sample appear associated with individual galaxies, the majority (78%) are associated with large-scale filamentary structures of galaxies, while 22% are found in galaxy "voids". Amongst the highest column density absorbers (with N_HI≈ 10¹⁶ cm^-2) in our sample, we find a low-ionization, metal-bearing absorber associated with a post-starburst dwarf galaxy ∼ 70h^-1₇₀ kpc away. The detailed properties of the absorber and the galaxy provide strong evidence that these two are causally related. We argue that many/most weak metal absorption systems could be due to outflowing "superwinds" from dwarf galaxies.