Detection of hot, metal-enriched outflowing gas around z ≈ 2.3 star-forming galaxies in the Keck Baryonic Structure Survey

We use quasar absorption lines to study the physical conditions in the circumgalactic medium of redshift z approximate to 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 Si IV is strongly enhanced within |Delta nu| less than or similar to 170 km s(-1) and projected distances broken vertical bar d broken vertical bar less than or similar to 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 Si IV optical depths, and that this enhancement extends out to similar to 350 km s(-1). At fixed HI the increase in themedian OVI optical depth near galaxies is 0.3-0.7 dex and is detected at 2-3 sigma confidence for all seven HI bins that have log(10) tau(HI) >= - 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 tau(HI) greater than or similar to 10. However, for pixels with tau(HI) less than or similar to 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 > 10(5) K) and that a substantial fraction of the hot gas has a metallicity greater than or similar to 10(-1) of solar. Given the high metallicity and large velocity extent (out to similar to 1.5 nu(circ)) of this gas, we conclude that we have detected hot, metal-enriched outflows arising from star-forming galaxies.