COS spectra of a Filament in NGC1275 - Testing the Particle Heating Mechanism

Halpha filaments are common in and around the brightest central galaxy in cool-core clusters of galaxies. A spectacular example occurs around NGC1275 in the nearby Perseus cluster. The low ionization spectrum of the filaments does not match that of any Galactic nebula and is not explained by any plausible photoionizing source. We have shown that the spectrum can be accounted for by ionization and excitation by ionizing particles, produced as the surrounding hot gas particles interpenetrate the cold atomic and molecular filament gas. Strong CI 1656A emission is predicted, as is HeII 1640A and a distinctive continuum. These, and other lines in the UV are sensitive to the energy injection mechanism. We propose to obtain a FUV spectrum of the outer horseshoe filament in the Perseus Cluster, using COS, to detect and measure these lines and the continuum to determine how these filaments are powered.