2007MNRAS.382.1246J

We present Spitzer high-resolution spectra of off-nuclear regions in the central cluster galaxies NGC1275 and NGC4696 in the Perseus and Centaurus clusters, respectively. Both objects are surrounded by extensive optical emission-line filamentary nebulae, bright outer parts of which are the targets of our observations. The 10-37µm spectra show strong pure-rotational lines from molecular hydrogen revealing a molecular component to the filaments which has an excitation temperature of ∼300-400K. The flux in the 0-0 S(1) molecular hydrogen line correlates well with the strength of the optical lines, having about 3 per cent of the Hα+[NII] emission. The 11.3-µm polycyclic aromatic hydrocarbon feature is seen in some spectra. Emission is also seen from both low- and high-ionization fine-structure lines. Molecular hydrogen cooler than ∼400K dominates the mass of the outer filaments; the nebulae are predominantly molecular.