The CGM2 Survey: Quenching and the Transformation of the Circumgalactic Medium

Abstract

This study addresses how the incidence rate of strong O vi absorbers in a galaxy’s circumgalactic medium (CGM) depends on galaxy mass and, independently, on the amount of star formation in the galaxy. We use Hubble Space Telescope/Cosmic Origins Spectrograph absorption spectroscopy of quasars to measure O vi absorption within 400 projected kpc and 300 km s ^−1 of 52 galaxies with M _* ∼ 3 × 10 ^10 M _⊙ . The galaxies have redshifts 0.12 < z < 0.6, stellar masses 10 ^10.1 M _⊙ < M _* < 10 ^10.9 M _⊙ , and spectroscopic classifications as star-forming or passive. We compare the incidence rates of high column density O vi absorption ( N _O _VI ≥ 10 ^14.3 cm ^−2 ) near star-forming and passive galaxies in two narrow ranges of stellar mass and, separately, in a matched range of halo mass. In all three mass ranges, the O vi covering fraction within 150 kpc is higher around star-forming galaxies than around passive galaxies with greater than 3 σ -equivalent statistical significance. On average, the CGM of star-forming galaxies with M _* ∼ 3 × 10 ^10 M _⊙ contains more O vi than the CGM of passive galaxies with the same mass. This difference is evidence for a CGM transformation that happens together with galaxy quenching and is not driven primarily by halo mass.

Keywords

• Circumgalactic medium
• Extragalactic astronomy
• Quenched galaxies