XMM-Newton observations of NGC 3268 in the Antlia Galaxy Cluster: characterization of a hidden group of galaxies at z ~0.41

Abstract

We report on a detailed X-ray study of the extended emission of the intracluster medium (ICM) around NGC3268 in the Antlia Cluster of galaxies, together with a characterization of an extended source in the field, namely a background cluster of galaxies at z ~ 0.41, which was previously accounted as an X-ray point source. The spectral properties of the extended emission of the gas present in Antlia were studied using data from the XMM-Newton satellite, complemented with optical images of Cerro Tololo Inter-American Observatory (CTIO) Blanco telescope, to attain for associations of the optical sources with the X-ray emission. The XMM-Newton observations show that the intracluster gas is concentrated in a region centred in one of the main galaxies of the cluster, NGC3268. By means of a spatially resolved spectral analysis, we derived abundances of the ICM plasma. We found a wall-like feature in the north-east direction, where the gas is characterized by a lower temperature with respect to the rest of the ICM. Furthermore, using combined optical observations, we inferred the presence of an elliptical galaxy in the centre of the extended X-ray source considered as a background cluster, which favours this interpretation.