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 ∼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 (∼4R_vir) from the nearest detected galaxy. Further, we find ∼50% 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.