Deep high-resolution X-ray spectra from cool-core clusters
  We examine deep XMM-Newton Reflection Grating Spectrometer (RGS) spectra from
the cores of three X-ray bright cool core galaxy clusters, Abell 262, Abell
3581 and HCG 62. Each of the RGS spectra show Fe XVII emission lines indicating
the presence of gas around 0.5 keV. There is no evidence for O VII emission
which would imply gas at still cooler temperatures. The range in detected gas
temperature in these objects is a factor of 3.7, 5.6 and 2 for Abell 262, Abell
3581 and HCG 62, respectively. The coolest detected gas only has a volume
filling fraction of 6 and 3 per cent for Abell 262 and Abell 3581, but is
likely to be volume filling in HCG 62. Chandra spatially resolved spectroscopy
confirms the low volume filling fractions of the cool gas in Abell 262 and
Abell 3581, indicating this cool gas exists as cold blobs. Any volume heating
mechanism aiming to prevent cooling would overheat the surroundings of the cool
gas by a factor of 4. If the gas is radiatively cooling below 0.5 keV, it is
cooling at a rate at least an order of magnitude below that at higher
temperatures in Abell 262 and Abell 3581 and two-orders of magnitude lower in
HCG 62. The gas may be cooling non-radiatively through mixing in these cool
blobs, where the energy released by cooling is emitted in the infrared. We find
very good agreement between smooth particle inference modelling of the cluster
and conventional spectral fitting. Comparing the temperature distribution from
this analysis with that expected in a cooling flow, there appears to be a even
larger break below 0.5 keV as compared with previous empirical descriptions of
the deviations of cooling flow models.
