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SEARCHING FOR COOLING FLOWS Silvia Caffi IASF/CNR Sez. Milano

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X-RAY SPECTRA: emission from optically thin thermal plasma polluted by heavy elements emission from optically thin thermal plasma polluted by heavy elements typical values: n e ~ 10 -4 10 -2 cm -3, T g ~ 10 7 10 8 K (heavily ionized gas), R ~ 1 Mpc. typical values: n e ~ 10 -4 10 -2 cm -3, T g ~ 10 7 10 8 K (heavily ionized gas), R ~ 1 Mpc. No absorption Exponential cut-off IMAGING: central regions feature ~ constant surface brightness central regions feature ~ constant surface brightness in outer regions S.B. falls off as a power-law with index ~ 3 in outer regions S.B. falls off as a power-law with index ~ 3 emission is traced out to 1-2 Mpc from the core emission is traced out to 1-2 Mpc from the core

Slide 3

Properties of the Intra Cluster Medium: hot, heavely ionized and tenouos gas at rest in the potential well of the cluster hot, heavely ionized and tenouos gas at rest in the potential well of the cluster dissipates energy at a very slow rate by X rays dissipates energy at a very slow rate by X rays considered as a fluid in hydrostatic equilibrium considered as a fluid in hydrostatic equilibrium

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t cool ~ T g 1/2 n p -1 for large radii n p is small for large radii n p is small in the core n p is large in the core n p is large t cool