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 ≈ 2.3 star-forming galaxies taken from the Keck Baryonic Structure Survey (KBSS). In Turner et al. (2014) 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 │Δv│≾. 170 km s^(-1) and projected distances │d│≾. 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^(-1). At fixed HI the increase in the median OvI optical depth near galaxies is 0.3-0.7 dex and is detected at 2-3-σ confidence for all seven HI bins that have log_(10) T_(HI) ≥ -1.5. We use ionisation models to show that the observed strength of OvI as a function of HI is consistent with enriched, photoionised gas for pixels with T_(HI) ≳ 10. However, for pixels with T_(HI) ≾ 1 this would lead to implausibly high metallicities at low densities if the gas were photoionised by the background radiation. This indicates that the galaxies are surrounded by gas that is sufficiently hot to be collisionally ionised (T > 10^5 K) 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 ~ 1.5 x v_(circ)) of this gas, we conclude that we have detected hot, metal enriched outflows arising from star-forming galaxies.
© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 April 2. Received 2015 April 2. In original form 2014. October 30. First published online April 30, 2015. We are very grateful to Milan Bogosavljevic, Alice Shapley, Dawn Erb, Naveen Reddy, Max Pettini, Ryan Trainor, and David Law for their invaluable contributions to the Keck Baryonic Structure Survey, without which the results presented here would not have been possible. We also thank Ryan Cooke for his help with the continuum fitting of QSO spectra. We gratefully acknowledge support from Marie Curie Training Network CosmoComp (PITN-GA-2009-238356) and the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement 278594-GasAroundGalaxies. CCS, GCR, ALS acknowledge support from grants AST-0908805 and AST-13131472 from the US National Science Foundation. We thank the W. M. Keck Observatory staff for their assistance with the observations. We also thank the Hawaiian people, as without their hospitality the observations presented here would not have been possible.
Submitted - 1410.8214v1.pdf
Published - MNRAS-2015-Turner-2067-82.pdf