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

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Abstract
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 ~ 1014.5-1015.5 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☉ and neutral hydrogen column density N < 1013.5 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☉. Finally, in clouds of N ~ 1014.5 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 ≤ 1013.5 cm-2.