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We present observations in CO(3-2) that, combined with previous observationsin CO(2-1), constrain the physical properties of the filamentary molecular gasin the central $\sim$6.5 kpc of NGC 1275, the central giant elliptical galaxyof the Perseus cluster. We find this molecular gas to have a temperature$\gtrsim 20$ K and a density $\sim$$10^2$-$10^4 {\rm \ cm^{-3}}$, typicallywarmer and denser than the bulk of Giant Molecular Clouds (GMCs) in the Galaxy.Bathed in the harsh radiation and particle field of the surroundingintracluster X-ray gas, the molecular gas likely has a much higher ionizationfraction than that of GMCs. For an ionization fraction of $\sim$$10^{-4}$,similar to that of Galactic diffuse ($\lesssim 250 {\rm \ cm^{-3}}$)partially-molecular clouds that emit in HCN(1-0) and HCO$^+$(1-0), we show thatthe same gas traced in CO can produce the previously reported emissions inHCN(3-2), HCO$^+$(3-2), and CN(2-1) from NGC 1275; the dominant source ofexcitation for all the latter molecules is collisions with electrons. Toprevent collapse, as evidenced by the lack of star formation in the molecularfilaments, they must consist of thin strands that have cross-sectional radii$\lesssim$0.2-2 pc if supported solely by thermal gas pressure; larger radiiare permissible if turbulence or poloidal magnetic fields provide additionalpressure support. We point out that the conditions required to relate COluminosities to molecular gas masses in our Galaxy are unlikely to apply incluster central elliptical galaxies. Rather than being virialized structuresanalogous to GMCs, we propose that the molecular gas in NGC 1275 comprisespressure-confined structures created by turbulent flows.

Role of Electon Excitation and Nature of Molecular Gas in Cluster Central Elliptical Galaxies