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Abstract

We present a spectral analysis of cool and cooling gas in 45 cool-core clusters and groups of galaxies obtained from Reflection Grating Spectrometer (RGS) XMM–Newton observations. The high-resolution spectra show Fe xvii emission in many clusters, which implies the existence of cooling flows. The cooling rates are measured between the bulk intracluster medium temperature and 0.01 keV and are typically weak, operating at less than a few tens of M_⊙yr⁻¹ in clusters and less than 1  M_⊙yr⁻¹ in groups of galaxies. They are 10–30 per cent of the classical cooling rates in the absence of heating, which suggests that active galactic nucleus feedback has a high level of efficiency. If cooling flows terminate at 0.7 keV in clusters, the associated cooling rates are higher, and have a typical value of a few to a few tens of M_⊙yr⁻¹ ⁠. Since the soft X-ray emitting region, where the temperature kT < 1 keV, is spatially associated with H α nebulosity, we examine the relation between the cooling rates above 0.7 keV and the H α nebulae. We find that the cooling rates have enough energy to power the total ultraviolet–optical luminosities, and are 5 to 50 times higher than the observed star formation rates for low-luminosity objects. In four high-luminosity clusters, the cooling rates above 0.7 keV are not sufficient and an inflow at a higher temperature is required. Further residual cooling below 0.7 keV indicates very low complete cooling rates in most clusters.