Strongly time-variable ultraviolet metal-line emission from the circum-galactic medium of high-redshift galaxies

We use cosmological simulations from the Feedback In Realistic Environments project, which implement a comprehensive set of stellar feedback processes, to study ultraviolet (UV) metal-line emission from the circum-galactic medium of high-redshift (z = 2–4) galaxies. Our simulations cover the halo mass range M h ∼ 2 × 1011–8.5 × 1012 M⊙ at z = 2, representative of Lyman break galaxies. Of the transitions we analyse, the low-ionization C iii (977 Å) and Si iii (1207 Å) emission lines are the most luminous, with C iv (1548 Å) and Si iv (1394 Å) also showing interesting spatially extended structures. The more massive haloes are on average more UV-luminous. The UV metal-line emission from galactic haloes in our simulations arises primarily from collisionally ionized gas and is strongly time variable, with peak-to-trough variations of up to ∼2 dex. The peaks of UV metal-line luminosity correspond closely to massive and energetic mass outflow events, which follow bursts of star formation and inject sufficient energy into galactic haloes to power the metal-line emission. The strong time variability implies that even some relatively low-mass haloes may be detectable. Conversely, flux-limited samples will be biased towards haloes whose central galaxy has recently experienced a strong burst of star formation. Spatially extended UV metal-line emission around high-redshift galaxies should be detectable by current and upcoming integral field spectrographs such as the Multi Unit Spectroscopic Explorer on the Very Large Telescope and Keck Cosmic Web Imager.