QUANTITATIVE SIGNATURES OF GALACTIC SUPERWINDS ON Lyα CLOUDS AND METAL-LINE SYSTEMS

摘要

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 ACDM model. Simulations produce metals self-consistently, based on one single parameter, the metal yield, which in turn is constrained by metallicity in the intra-cluster 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 10~(12)-10~(14) cm~(-2). We find that the number density of Lyα lines with metallicity Z ≥ 10~(-3) Z_☉ 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 atz ～ 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_(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).