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Scattering of emission lines in galaxy cluster cores: measuring electron temperature

The central galaxies of some clusters can be strong emitters in the Ly$α$ and H$α$ lines. This emission may arise either from the cool/warm gas located in the cool core of the cluster or from the bright AGN within the central galaxy. The luminosities of such lines can be as high as $10^{42} - 10^{44}$ erg/s. This emission originating from the core of the cluster will get Thomson scattered by hot electrons of the intra-cluster medium (ICM) with an optical depth $\sim$ 0.01 giving rise to very broad ($Δλ/ λ\sim$ 15%) features in the scattered spectrum. We discuss the possibility of measuring the electron density and temperature using information on the flux and width of the highly broadened line features.