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OF GALACTIC OUTFLOWS AS ABSORPTION-FREE GAPS IN THE LY α FOREST

Powerful outflows from star-forming galaxies are expected to push away the neutral intergalactic medium (IGM) around those galaxies, and produce absorption-free gaps in the Lyα forest. We analyze the abundance of gaps of various sizes in three high resolution spectra of quasars at z ∼ 3 – 3.5. The gap statistics agrees well with a model in which galactic halos above a minimum mass scale of Mmin ∼ 10 10 M⊙ produce bubbles with a characteristic radius of Rb ∼ 0.48h −1 Mpc. Both numbers are consistent with naive theoretical expectations, where the minimum galaxy mass reflects the threshold for infall of gas out of a photo-ionized IGM. The observed gaps are typically bounded by deep absorption features as expected from the accumulation of swept-up gas on the bubble walls. Subject headings: large-scale structure of the universe — intergalactic medium — quasars: absorption lines — cosmology: theory