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We announce a new facility in the spectral code CLOUDY that enables trackingthe evolution of a cooling parcel of gas with time. For gas cooling fromtemperatures relevant to galaxy clusters, earlier calculations estimated the[Fe XIV] {\lambda}5303 / [Fe X] {\lambda}6375 luminosity ratio, a criticaldiagnostic of a cooling plasma, to slightly less than unity. By contrast, ourcalculations predict a ratio ~3. We revisit recent optical coronal lineobservations along the X-ray cool arc around NGC 4696 by Canning et al. (2011),which detected [Fe X] {\lambda}6375, but not [Fe XIV] {\lambda}5303. We showthat these observations are not consistent with predictions of cooling flowmodels. Differential extinction could in principle account for theobservations, but it requires extinction levels (A_V > 3.625) incompatible withprevious observations. The non-detection of [Fe XIV] implies a temperatureceiling of 2.1 million K. Assuming cylindrical geometry and transonic turbulentpressure support, we estimate the gas mass at ~1 million solar masses. Thecoronal gas is cooling isochorically. We propose that the coronal gas has notcondensed out of the intracluster medium, but instead is the conductive ormixing interface between the X-ray plume and the optical filaments. We presenta number of emission lines that may be pursued to test this hypothesis andconstrain the amount of intermediate temperature gas in the system.

Implications of Coronal Line Emission in NGC 4696