CEA News, September 2018

Tracing oxygen in the halos of distant galaxies with the Quasar and Galaxy Evolution Survey

Galaxies and their environments are both highly dynamic - interacting, changing and evolving. Only part of this is seen with the optical light that is primarily emitted by the stars within galaxies. Indeed, galaxies are embedded in enormous halos of gas, which play host a wide range of the physics that moulds galaxy formation.

Astronomers from the CEA are leading a new survey to study these gaseous halos, known as the circum-galactic medium. A new paper released this month presents the first steps in this survey, centred on ~100 orbits of observations with the Hubble Space Telescope. Using grism spectroscopy, the Quasar Sightline and Galaxy Evolution (or QSAGE) survey maps the positions and properties of 1000s of galaxies across 12 fields (the first field is shown in the left hand panel in the image) in the foreground of bright distant QSOs. Combining the galaxy data with backgound QSOs (whose light reveals the complex gas structures around each galaxy) QSAGE provides an unparalleled data resource for studying galaxy halo gas in the Universe's middle ages.

In the first paper, QSAGE takes a look at the oxygen levels withn the galaxy halo environment, finding large quantities of highly ionised oxygen (O5+) around massive star- forming galaxies (shown in the right hand panel in the image) as well as being associated with a low mass group of galaxies within the survey region.

The scientific paper in full can be accessed at: arXiv/1809.05544.