The detailed nature of active central cluster galaxies

Abstract

We present detailed integral field unit observations of the central few kiloparsecs of the ionized nebulae surrounding four active central cluster galaxies (CCGs) in cooling flow clusters (Abell 0496, 0780, 1644 and 2052). Our sample consists of CCGs with Hα filaments, and have existing data from the X-ray regime available. Here, we present the detailed optical emission-line (and simultaneous absorption line) data over a broad wavelength range to probe the dominant ionization processes, excitation sources, morphology and kinematics of the hot gas (as well as the morphology and kinematics of the stars). This, combined with the other multiwavelength data, will form a complete view of the different phases (hot and cold gas and stars) and how they interact in the processes of star formation and feedback detected in central galaxies in cooling flow clusters, as well as the influence of the host cluster. We derive the optical dust extinction maps of the four nebulae.We also derive a range of different kinematic properties, given the small sample size. For Abell 0496 and 0780, we find that the stars and gas are kinematically decoupled, and in the case of Abell 1644 we find that these components are aligned. For Abell 2052, we find that the gaseous components show rotation even though no rotation is apparent in the stellar components. To the degree that our spatial resolution reveals, it appears that all the optical forbidden and hydrogen recombination lines originate in the same gas for all the galaxies. Based on optical diagnostic ratios ([O III] λ5007/Hβ against [N II] λ6584/Hα, [SII] λλ6717, 6731/Hα and [O I] λ6300/Hα), all galaxies show extended low-ionization nuclear emission-line region emission, but that at least one has significant Seyfert emission areas, and at least one other has significant HII-like emission line ratios for many pixels. We also show that the hardness of the ionizing continuum do not decrease with galactocentric distance within our field-of-view (with the exception of one galaxy that show a core separation) as the emission line ratios do not vary significantly with radius. This also indicates that the derived nebular properties are spatially homogeneous. We fit active galactic nucleus (AGN) and post-asymptotic giant branch (pAGB) stars photoionization models as well as shock excitation models to our derived diagnostic ratios. These fits, combined with information from multiwavelength studies, reveal that AGN photoionization is the most likely ionization mechanism in at least two cases even though shocks and pAGB stars cannot be conclusively eliminated.