Resolving the Role of Environment in Shaping the Circumgalactic Media Around Massive Galaxies

The circumgalactic medium (CGM) — the ~ 100 kpc region surrounding a typical galaxy — is a reservoir of diffuse gas thought to be crucial to the long-term regulation of star formation activity within galaxies. However, the physical mechanisms through which the CGM affects the baryon cycle and galaxy evolution are still poorly understood, particularly with regard to massive quiescent galaxies. In this project, we study the gaseous environment of the massive lensing galaxy WFI 2033-4723 (z ~ 0.66) using absorption spectroscopy with the aid of a quadruply lensed quasar (z ~ 1.66), which gives us a unique opportunity to seek absorption along four lines of sight and investigate the spatial variations in CGM gas properties. Using wide-field deep integral-field spectroscopic data from the MUSE spectrograph of the European Southern Observatory’s 8.2m VLT-4 Telescope, we identify three galaxies within dv < 700 km/s and with projected physical separations of < 200 kpc with respect to the lens, indicating that it belongs to a dense group environment. Based on spectral indices, we estimate star formation rates (SFR) and stellar population ages for these galaxies, finding that they are old (~1 Gyr) and relatively non-starforming, with the lensing galaxy being particularly quiescent. We probe the CGM of the lens using additional high-resolution echelle spectra of the four quasar sightlines from the MIKE spectrograph of Las Campanas Observatory’s Clay Telescope. We find MgII and FeII absorption in only 1 of 4 sightlines, suggesting that the covering fraction of the cool (~10 K) gas 4 containing these species is lower in massive galaxies which are situated in a dense galactic environment. This project directly considers the role that the galaxy environment may play in determining the properties of the CGM, in hopes of providing further clues into the relationship between the CGM and galaxy evolution. Future work probing more lens systems will allow us to systematically quantify the role of the galaxy environment in shaping the properties of galaxies and the CGM.