Investigating the Hot Gas in Active Brightest Cluster Galaxies

Abstract

We investigate a crucial phase in the cooling-feedback cycle in the star forming Brightest Cluster Galaxies (BCGs) by looking at the optical emission line properties of the reheated gas that ultimately causes the cycle to repeat. We investigate the source, or the mixture of sources, of ionization of the gas. To identify the dominant ionization processes, excitation sources, morphology and kinematics of the hot gas, line ratios over the entire optical wavelength range are necessary. For this purpose, the spatially-resolved spectra over the entire optical wavelength range for eight nearby, active BCGs in X-ray luminous groups and clusters have been obtained with the Southern African Large Telescope (SALT). The BCG sample was chosen to have H$\alpha$ detections - a strong indication of star formation activity, as well as existing hot cluster data from X-ray regime available. The fundamental gas properties such as electron density, gas temperature, metallicity and several abundances were derived using the spectral features across the long wavelength range. The present optical data will be combined with the other multi-wavelength data to form a complete view of the different phases (hot and cold gas and young stars) and how they interact in the processes of star formation and feedback detected in central galaxies in cooling flow systems, as well as the influence of the surrounding intracluster medium (ICM). Here we present our preliminary results on one of those eight BCGs, Hydra A, which shows the complexity and spatial variation of the ionization mechanisms in the nucleus.