Absorption features of high-redshift galactic winds

The environment of high-redshift galaxies is characterized by both wind-driven outflowing gas and gravitationally infalling streams. To investigate such galaxy–IGM interplay we have generated synthetic optical absorption line spectra piercing the volume surrounding a starbursting analogue of a Lyman-break galaxy selected in a z≈ 3 output from a smoothed particle hydrodynamics simulation, including a detailed treatment of mechanical feedback from winds. Distributions for several observable species (H i, C iii, C iv, Si ii, Si iii, Si iv, O vi, O vii and O viii) have been derived by post-processing the simulation outputs. The hot-wind material is characterized by the presence of high-ionization species such as O vi, O vii and O viii (the latter two observable only in X-ray bands); the colder (T < 105.5 K) infalling streams can be instead identified by the combined presence of Si ii, Si iii and C iii optical absorption together with O vi that surrounds the cooler gas clumps. However, both line profile and pixel optical depth analysis of the synthetic spectra show that the intergalactic filament in which the wind-blowing galaxy is embedded produces absorption signatures that closely mimic those of the wind environment. We conclude that it may be difficult to clearly identify wind-blowing galaxies and their complex gaseous environment at high redshift in optical QSO absorption-line spectra based solely on the observed ion-absorption patterns.