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 × 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 (∼4Rvir) from the nearest detected galaxy. Further, we find ∼50% of 1 M· yr-1 star-forming galaxies within 2Rvir show no associated O vi absorption to a limit of at least N(O vi) = 1013.9 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· ∼109.5-10 M· mass galaxies (Mhalo ∼1011.5-12 M· dark matter haloes), and infer that they may be tracing predominantly collisionally ionized gas within the haloes of such galaxies.
- galaxies: distances and redshifts
- intergalactic medium
- quasars: absorption lines