Quantitative Signatures of Galactic Superwinds on Lyα Clouds and Metal-Line Systems

We investigate possible signatures of feedback from galactic superwinds (GSWs) on the metallicity of the Lyα forest, using a set of high-resolution hydrodynamic simulations of a ΛCDM model. Simulations produce metals self-consistently, based on one single parameter, the metal yield, which in turn is constrained by metallicity in the intracluster gas. We follow metals as a separate density species. The metallicity of Lyα clouds having column density of N_HI~10^14.5-10^15.5 cm^-2 at z=2-4 is correctly predicted by simulations, both with and without GSWs, implying an in situ origin for these metals. However, a unique signature and sensitive test of GSWs are provided by lower column density clouds of 10¹²-10¹⁴ cm^-2. We find that the number density of Lyα lines with metallicity Z>=10^-3 Z_solar and neutral hydrogen column density N_HI<10^13.5 cm^-2 provides a first quantitative measure of the strength of GSWs, because metals in these systems are a contaminant. We predict that the number of such lines per unit redshift at z~3 should be about 0.1 in the absence of GSWs. With the observed GSW strength, we expect to see 20-50 such lines per unit redshift. This is an observational challenge. Furthermore, we find that the difference between simulations with and without GSWs becomes much larger with regard to a subset of such clouds with high Doppler widths, since the contaminated systems are considerably hotter than the normal IGM. We also present preliminary results on C IV and O VI lines as a function of GSW strength. The filling factor of metal-rich regions is a strong function of GSWs. With and without GSWs the volume filling factor is 6.0%, 4.2%, and 1.9% and 1.0%, 0.28%, and 0.08%, respectively, for regions with metallicity greater than 10^-3, 10^-2, and 10^-1 Z_solar. Finally, in clouds of N_HI~10^14.5 cm^-2, we predict that the ratio of secondary (e.g., N) to primary metals (e.g., O, C) is expected to be smaller by a factor of 10 than in large galaxies, which better retain metals; this factor increases to >=50 for N_HI<=10^13.5 cm^-2.