COSHalos
COSHalos, commonly written as COS-Halos, is a spectroscopic survey that studied the circumgalactic medium (CGM) of galaxies in the low-redshift universe using ultraviolet absorption-line spectroscopy with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope. The project aimed to characterize the gas content, metallicity, ionization state, and spatial extent of halo gas around ordinary (L*) galaxies and to understand how CGM properties relate to star formation and galaxy evolution.
Methods and scope: The program used background quasars and active galactic nuclei whose sightlines pass near
Key findings: COS-Halos demonstrated that halo gas around L*-type galaxies is rich in both neutral and ionized
Impact: The COS-Halos results provided critical empirical constraints on models of the baryon cycle and feedback
See also: Circumgalactic medium; Hubble Space Telescope; Cosmic Origins Spectrograph; galaxy evolution. References include key publications