Discovery of atomic and molecular mid infra - red emission lines in off - nuclear regions of NGC 1275 and NGC 4696 with the Spitzer Space Telescope

We present Spitzer high-resolution spectra of off-nuclear regions in the central cluster galaxies NGC 1275 and NGC 4696 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. Emission is also seen from both low and high ioniza-tion fine structure lines. Cold molecular hydrogen dominates the mass of the outer filaments; the nebulae are predominantly molecular.