Quasar Sightline and Galaxy Evolution (QSAGE) Survey - I. The Galaxy Environment of OVI Absorbers up to z=1.4 around PKS 0232-04

• Main Authors: Bielby, R. M, Stott, J. P, Cullen, F, Tripp, T. M, Burchett, J, Fumagalli, M, Morris, S. L, Tejos, N, Crain, R. A, Bower, R. G, Prochaska, J. X
• Format: Journal Article
• Language: English
• Published: 14-09-2018
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.1809.05544

We present the first results from a study of OVI absorption around galaxies
at $z<1.44$ using data from a near-infrared grism spectroscopic Hubble Space
Telescope Large Program, the Quasar Sightline and Galaxy Evolution (QSAGE)
survey. QSAGE is the first grism galaxy survey to focus on the circumgalactic
medium at $z\sim1$, providing a blind survey of the galaxy population. Using
the first of 12 fields, we provide details of the reduction methods, in
particular the handling of the deep grism data which uses multiple position
angles to minimise the effects of contamination from overlapping traces. The
resulting galaxy sample is H$\alpha$ flux limited ($f({\rm H\alpha}) >
2\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$) at 0.68<z<1.44, corresponding to
$\gtrsim0.2-0.8$ M$_\odot$ yr$^{-1}$. We combine the galaxy data with
high-resolution STIS and COS spectroscopy of the background quasar to study OVI
in the circumgalactic medium. At z>0.68, we find 5 OVI absorption systems along
the line of sight with identified galaxies lying at impact parameters of
$b\approx100-350$ kpc (proper), whilst we find a further 13 galaxies with no
significant associated OVI absorption (i.e. $N({\rm OVI})<10^{13.5-14}$
cm$^{-2}$) in the same impact parameter and redshift range. We find a large
scatter in the stellar mass and star-formation rates of the closest galaxies
with associated OVI. Whilst one of the OVI absorber systems is found to be
associated with a low mass galaxy group at $z\approx1.08$, we infer that the
detected OVI absorbers typically lie in the proximity of dark matter halos of
masses $10^{11.5} {\rm M_\odot}\lesssim M_{\rm halo}\lesssim10^{12} {\rm
M_\odot}$.