Galactic wind effects on the Lyα absorption in the vicinity of galaxies

We present predictions of Ly alpha forest-galaxy correlations at z = 3 from Eulerian simulations that include the effects of galactic winds, driven primarily by supernova explosions. Galactic winds produce expanding bubbles of shock-heated gas within similar to 0.5 comoving h(-1) Mpc of luminous galaxies in the simulation, which have space density similar to that of observed Lyman break galaxies (LBGs). However, most of the low-density intergalactic gas that determines the observed properties of the Ly alpha forest is unaffected by winds. The impact of winds on the Ly alpha optical depth near galaxies is less dramatic than their impact on gas temperature, because winds heat only a small fraction of the gas present in the turnaround regions surrounding galaxies. Hence, Ly alpha absorption from gas outside the wind bubbles is spread out over the same velocity range occupied by the wind-heated gas. In general, Ly alpha absorption is expected to be stronger than average near galaxies because of the high gas density. Winds result in a modest reduction of this expected increase of Ly alpha absorption. Our predictions can be compared to future observations to detect the wind effects and infer their strength, although with the caveat that the results are still dependent on the correspondence of simulated galaxies and observed LBGs. We find that wind effects in our simulations are not strong enough to reproduce the high Ly alpha transmission within 0.5 h(-1) Mpc comoving of galaxies that has been suggested by recent observations; powerful galactic explosions or ejecta with hyper-escape velocities would be required, but these are unlikely to be produced by ordinary star formation and supernovae alone.