Detection of optical coronal emission from 106-K gas in the core of the Centaurus cluster

R Canning, A Fabian, R Johnstone, J Sanders, C Crawford, N Hatch, G Ferland
2011 Monthly Notices of the Royal Astronomical Society   unpublished
We report a detection (3.5 × 10 37 ± 5.6 × 10 36 erg s −1 ) 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 × 10 6 −5 × 10 6 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
more » ... observations (∼10 M yr −1 ); however, we detect twice the luminosity expected for [Fe X] λ6374 emission, at 10 6 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 × 10 6 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.