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AIP Conference Proceedings


Hydrodynamic cosmological simulations predict that the average opacity of the Ly forest should increase in the neighborhood of galaxies because galaxies form in dense environments. Recent observations (Adelberger et al. [1]) confirm this expectation at large scales, but they show a decrease of absorption at comoving separations r 1h–1 Mpc. We show that this discrepancy is statistically significant, especially for the innermost data point at r 0.5h–1, even though this data point rests on three galaxy-quasar pairs. Galaxy redshift errors of the expected magnitude are insufficient to resolve the conflict. Peculiar velocities allow gas at comoving distances 1h–1 Mpc to produce saturated absorption at the galaxy redshift, putting stringent requirements on any "feedback" solution. Local photoionization is insufficient, even if we allow for recurrent AGN activity that keeps the neutral hydrogen fraction below its equilibrium value. A simple "wind" model that eliminates all neutral hydrogen in spheres around the observed galaxies can marginally explain the data, but only if the winds extend to comoving radii ~ 1.5h–1 Mpc.


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