How do galactic winds affect the Lyα forest?

We investigate the effect of galactic winds on the Lyα forest in cosmological simulations of structure and galaxy formation. We combine high resolution N-body simulations for the evolution of the dark matter with a semi-analytic model for the formation and evolution of galaxies which includes detailed prescriptions for the long-term evolution of galactic winds. We find that the main statistical properties of the Lyα forest, namely the power spectrum P (k) and the flux probability distribution function (PDF), are not significantly affected by winds and do not give a unique answer when trying to rule out or constrain wind models. Winds expanding around galaxies do, however, produce detectable signatures in the forest, in the form of increased flux transmissivity inside hot bubbles and narrow, saturated absorption lines corresponding to dense cooled shells. We find that the Lyα flux transmissivity is highly enhanced in proximity of wind–blowing galaxies, which represent up to half the galaxies in our sample, in agreement with the results of Adelberger et al. 2005. We finally propose a new method to test for the presence of absorption lines due to wind shells in the Lyα forest: we calculate the number distribution of saturated regions in spectra as a function of their width and we find that the number of saturated regions with widths smaller than about 1 Å at z = 3 and 0.6 Å at z = 2 may be more than doubled. This effect should be clearly detectable in real spectra.