Metal Lines Associated with the Lyα Forest from eBOSS Data

We investigate the metal species associated with Ly$\alpha$ forest in eBOSS quasar spectra. Metal absorption lines are revealed stacked spectra from cross-correlating selected absorbers and flux fluctuation field. Up to 13 identified relatively strong (those $-1.0<\delta_{\rm Ly\alpha}<-0.6$ neutral hydrogen column density of ~ $10^{15-16}$ $\rm cm^{-2}$) over absorber redshift range $2<z_{\rm abs}<4$. The densities these decrease toward higher for weaker absorbers. From modelling various species, we find that pattern suggests contributions multiple gas components both circumgalactic medium (CGM) intergalactic (IGM). While low-ionization (e.g., C II, Si Mg II) can be explained by high-density, cool ($T \sim 10^4$ K) CGM, high-ionization may reside low-density or high-temperature IGM. measurements provide inputs model contamination baryon acoustic oscillations measurement. Comparison absorptions high-resolution hydrodynamic galaxy formation simulations further elucidate physical conditions