Are small-scale substructures a universal property of galaxy haloes? The case of the giant elliptical NGC5128

Abstract

We present an analysis of the spatial and chemical substructures in a remote halo field in the nearby giant elliptical galaxy CentaurusA (NGC5128), situated ~38kpc from the centre of the galaxy. The observations were taken with the Advanced Camera for Surveys instrument on-board theHubble Space Telescope, and reach down to the horizontal branch. In this relatively small 3.8 × 3.8kpc2 field, after correcting for Poisson noise, we do not find any statistically strong evidence for the presence of small-scale substructures in the stellar spatial distribution on scales ≳100pc. However, we do detect the presence of significant small spatial-scale inhomogeneities in the stellar median metallicity over the surveyed field. We argue that these localized chemical substructures could be associated with not fully mixed debris from the disruption of low-mass systems. NGC5128 joins the ranks of the late-type spiral galaxies the Milky Way, for which the stellar halo appears to be dominated by small-scale spatial substructures, and NGC891, where localized metallicity variations have been detected in the inner extraplanar regions. This suggests that the presence of small-scale substructures may be a generic property of stellar haloes of large galaxies. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.