Detection of optical coronal emission from 10^6 K gas in the core of the Centaurus cluster

TL;DR

This study detects optical coronal emission lines in the Centaurus cluster's core, indicating hot gas at 1-5 million K, and suggests heating processes rather than cooling dominate in this environment.

Contribution

First detection of optical coronal lines in the Centaurus cluster core, providing new insights into the thermal state and heating mechanisms of intracluster gas.

Findings

Detected [Fe X]6374 emission indicating 1 million K gas

Observed luminosity twice that expected from cooling models

No coronal lines from [Ca XV], implying calcium depletion onto dust

Abstract

We report a detection (3.5x10^37 \pm 5.6x10^36 ergps) of the optical coronal emission line [Fe X]6374 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 and 5 million 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 solar masses per year) however we detect twice the luminosity expected for [Fe X]6374 emission, at 1 million 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 million K gas seen near the centre in X-rays with Chandra. Calcium is however likely to be depleted from the gas phase onto dust grains in the central regions of NGC 4696.