Quasar Sightline and Galaxy Evolution (QSAGE) survey - I. The galaxy environment of O VI absorbers up to z=1.4 around PKS 0232-04

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 similar to 1, providing a blind survey of the galaxy population. The galaxy sample is H alpha flux limited (f(H alpha) > 2 x 10(-17) erg s(-1) cm(-2)) at 0.68 < z < 1.44, corresponding to greater than or similar to 0.2-0.8 M-circle dot 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 similar to 1, we find O VI absorption systems up to b similar to 350 kpc (similar to 4R(vir)) from the nearest detected galaxy. Further, we find similar to 50 per cent of greater than or similar to 1 M-circle dot 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) > 10(14) cm(-2)) O VI absorption systems to be associated with M-star similar to 10(9.5-10) M-circle dot mass galaxies (M-halo similar to 10(11.5-12) M-circle dot dark matter haloes), and infer that they may be tracing predominantly collisionally ionized gas within the haloes of such galaxies.