2019MNRAS.486...21B

We present the first results from a study of O VI absorption around galaxies at z < 1.44 using data from a near-infrared grism spectroscopic Hubble Space Telescope Large Programme, the Quasar Sightline and Galaxy Evolution (QSAGE) survey. QSAGE is the first grism galaxy survey to focus on the circumgalactic medium at z ∼ 1, providing a blind survey of the galaxy population. The galaxy sample is H α flux limited (f(H α) > 2 x 10^–17 erg s^–1 cm^–2) at 0.68 < z < 1.44, corresponding to >=0.2-0.8 M_☉ yr^–1. In this first of 12 fields, we combine the galaxy data with high-resolution STIS and COS spectroscopy of the background quasar to study O VI in the circumgalactic medium. At z ∼ 1, we find O VI absorption systems up to b ∼ 350 kpc (∼4R_vir) from the nearest detected galaxy. Further, we find ∼50 per cent of >=1 M_☉ yr^–1 star-forming galaxies within 2R_vir show no associated O VI absorption to a limit of at least N(O VI) = 10^13.9 cm^–2. That we detect O VI at such large distances from galaxies and that a significant fraction of star-forming galaxies show no detectable O VI absorption disfavours outflows from ongoing star formation as the primary medium traced by these absorbers. Instead, by combining our own low- and high-redshift data with existing samples, we find tentative evidence for many strong (N(O VI) > 10¹⁴ cm^–2) O VI absorption systems to be associated with M_* ∼ 10^9.5–10 M_☉ mass galaxies (M_halo ∼ 10^11.5–12 M_☉ dark matter haloes), and infer that they may be tracing predominantly collisionally ionized gas within the haloes of such galaxies.