The Chandra Fornax Survey. I. The Cluster Environment

We present the first results of a deep Chandra survey of the inner 61 of the Fornax cluster of galaxies. Ten 50 ks pointings were obtained in a mosaic centered on the giant elliptical galaxy NGC 1399 at the nominal cluster center. Emission and temperature maps of Fornax are presented, and an initial study of more than 700 detected X-ray point sources is made. Regions as small as 100 pc are resolved. The intracluster gas in Fornax exhibits a highly asymmetric morphology and temperature structure, dominated by a 180 kpc extended "plume" of low surface brightness, cool (,1 keV) gas to the northeast of NGC 1399 with a sharper edge to the southwest. The elliptical galaxy NGC 1404 also exhibits a cool halo of X-ray gas within the cluster, with a highly sharpened leading edge as it presumably falls into the cluster and a comet-like tail. We estimate that some 6200-400 point sources are physically associated with Fornax. Confirming earlier works, we find that the globular cluster population in NGC 1399 is highly X-ray active, extending to globular clusters that may in fact be intracluster systems. We have also found a remarkable correlation between the location of giant and dwarf cluster galaxies and the presence of X-ray counterparts, such that systems inhabiting regions of low gas density are more likely to show X-ray activity. Not only does this correlate with the asymmetry of the intracluster gas, but it also correlates with the axis joining the center of Fornax to an infalling group 1 Mpc to the southwest. We suggest that Fornax may be experiencing either an intergalactic "headwind" due to motion relative to the surrounding large-scale structure or that the intracluster medium has been disturbed relative to the overall cluster gravitational potential by previous activity.