2015MNRAS.450.2067T

We use quasar absorption lines to study the physical conditions in the circumgalactic medium of redshift z ~ 2.3 star-forming galaxies taken from the Keck Baryonic Structure Survey. In Turner et al. we used the pixel optical depth technique to show that absorption by Hi and the metal ions Ovi, Nv, Civ, Ciii, and Siiv is strongly enhanced within {verbar}Δv{verbar} ≲ 170 km/s and projected distances {verbar}d{verbar} ≲ 180 proper kpc from sightlines to the background quasars. Here we demonstrate that the Ovi absorption is also strongly enhanced at fixed Hi, Civ, and Siiv optical depths, and that this enhancement extends out to ∼ 350 km/s. At fixed Hi the increase in the median Ovi optical depth near galaxies is 0.3-0.7 dex and is detected at 2-3σ confidence for all seven Hi bins that have log_10τ_H  I ≥-1.5. We use ionization models to show that the observed strength of Ovi as a function of Hi is consistent with enriched, photoionized gas for pixels with τ_H  I \gtrsim 10. However, for pixels with τ_H  I \lesssim 1 this would lead to implausibly high metallicities at low densities if the gas were photoionized by the background radiation. This indicates that the galaxies are surrounded by gas that is sufficiently hot to be collisionally ionized (T > 10⁵K) and that a substantial fraction of the hot gas has a metallicity ≳ 10^–1 of solar. Given the high metallicity and large velocity extent (out to ∼ 1.5vcirc) of this gas, we conclude that we have detected hot, metal-enriched outflows arising from star-forming galaxies.