The X-ray emission properties and the dichotomy in the central stellar cusp shapes of early-type galaxies

The Hubble Space Telescope has revealed a dichotomy in the central surface brightness profiles of early-type galaxies, which have subsequently been grouped into two families: core, boxy, anisotropic systems; and cuspy ('power-law'), discy, rotating ones. Here we investigate whether a dichotomy is also present in the X-ray properties of the two families. We consider both their total soft emission (L-SX,L-tot), which is a measure of the galactic hot gas content, and their nuclear hard emission (L-HX,L- nuc), mostly coming from Chandra observations, which is a measure of the nuclear activity. At any optical luminosity, the highest L-SX,L- tot values are reached by core galaxies; this is explained by their being the central dominant galaxies of groups, subclusters or clusters, in many of the log L-SX,L- tot (erg s(-1)) greater than or similar to 41.5 cases. The highest L-HX,L- nuc values, similar to those of classical active galactic nuclei (AGNs), in this sample are hosted only by core or intermediate galaxies; at low luminosity AGN levels, L-HX,L- nuc is independent of the central stellar profile shape. The presence of optical nuclei (also found by HST) is unrelated to the level of L-HX,L- nuc, even though the highest L-HX,L- nuc are all associated with optical nuclei. The implications of these findings for galaxy evolution and accretion modalities at the present epoch are discussed.