As much of half the baryonic mass of galaxies are found in galactic halos rather than stars and visible objects. This mass is in a gaseous form known as the circumgalactic medium. Currently, it is theorised that cold gas with low metallicity resupplies galaxies by spiralling in along the galactic plane. Galaxies, in turn, eject gas which has much higher metallicity and temperatures. Recent observations tend to support this theory. However, the theory has only been tested against a small number of galaxies.
The properties of the CGM are determined using the absorption lines found in quasar spectra. These absorption lines arise from the gas in the CGM absorbing the light from background quasars. Properties such as metallicity, temperature, column density and the kinematics can be calculated from the spectra. It is then possible to determine the behaviour of the CGM and the surrounding galaxies. Previous research has focused on lone galaxies. I will be expanding the survey of galaxies to include those in clusters.
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