2011MNRAS.411..411C

We report a detection (3.5 x 10³⁷± 5.6 x 10³⁶ erg/s) of the optical coronal emission line [Fe X] λ6374 and upper limits of four other coronal lines using high-resolution VIMOS spectra centred on NGC 4696, the brightest cluster galaxy in the Centaurus cluster. Emission from these lines is indicative of gas at temperatures between 1 x 10⁶-5 x 10⁶ K, so traces the interstellar gas in NGC 4696. The rate of cooling derived from the upper limits is consistent with the cooling rate from X-ray observations ( ∼ 10 M_☉/yr); however, we detect twice the luminosity expected for [Fe X] λ6374 emission, at 10⁶ K, our lowest temperature probe. We suggest this emission is due to the gas being heated rather than cooling out of the intracluster medium. We detect no coronal lines from [Ca XV], which are expected from the 5 x 10⁶ K gas seen near the centre in X-rays with Chandra. Calcium is, however, likely to be depleted from the gas phase on to dust grains in the central regions of NGC 4696.