Cool X-ray emitting gas in the core of the Centaurus cluster of galaxies

We use a deep XMM–Newton Reflection Grating Spectrometer observation to examine the X-ray emission from the core of the Centaurus cluster of galaxies. We clearly detect Fe xvii emission at four separate wavelengths, indicating the presence of cool X-ray emitting gas in the core of the cluster. Fe ions from Fe xvii to xxiv are observed. The ratio of the Fe xvii 17.1 Å lines to 15.0 Å line and limits on O vii emission indicate a lowest detected temperature in the emitting region of 0.3 to 0.45 keV (3.5 to 5.2 × 106 K). The cluster also exhibits strong N vii emission, making it apparent that the N abundance is supersolar in its very central regions. Comparison of the strength of the Fe xvii lines with a solar metallicity cooling flow model in the inner 17 kpc radius gives mass deposition rates in the absence of heating of 1.6–3 M⊙ yr−1. Spectral fitting implies an upper limit of 0.8 M⊙ yr−1 below 0.4 keV, 4 M⊙ yr−1 below 0.8 keV and 8 M⊙ yr−1 below 1.6 keV. The cluster contains X-ray emitting gas over at least the range of 0.35 to 3.7 keV, a factor of more than 10 in temperature. We find that the best-fitting metallicity of the cooler components is smaller than the hotter ones, confirming that the apparent metallicity does decline within the inner 1 arcmin radius.