A Molecular Hydrogen Nebula in the Central cD Galaxy of the Perseus Cluster

We report narrowband imaging of the 1–0S(1) ro-vibrational transition of molecular hydrogen (H2) from NGC 1275, the central cD galaxy of the Perseus Cluster. We find that the H2 gas has a spatial morphology identical to the optical emission-line nebula associated with this galaxy, a total luminosity in H2 1–0 S(1) only an order of magnitude less than in Hα, and if the line-emitting gas is thermalized a mass (at ∼2000 K) that is over two orders of magnitude smaller than that of the optical emission-line nebula (at ∼10,000 K). The ratio in H2 1–0 S(1) to Hα +[ Nii] line intensities spans a characteristic range of ∼0.02–0.08 throughout the nebula; the brighter inner nebula exhibits patches with (nearly) constant line ratios unrelated to individual filaments. Recent models proposed to explain the peculiar nebular spectrum from the optical to infrared invoke thermalized along with non-thermalized injection of energy from ionizing particles. The energy density of highly relativistic electrons inferred to cause inverse-Compton scattering of hard X-ray emission from the core of the Perseus Cluster decreases steeply beyond a central radius of ∼20 kpc, yet we do not find any changes in the average or range spanned by the H2 1–0 S(1) to Hα +[ Nii] line ratio between the inner (20 kpc) and outer (∼20–50 kpc) nebulae. On the other hand, saturated conduction from the surrounding X-ray gas produces, in the absence of magnetic fields, a heat flux that is approximately constant throughout the nebula: the change in the line ratio with position would then reflect the ability of the X-ray gas to penetrate presumably magnetically threaded filaments at different locations.