Open AccessThe X‐ray emission properties and the dichotomy in the central stellar cusp shapes of early‐type galaxies
Author(s) -
Pellegrini S.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.09549.x
Subject(s) - physics , astrophysics , galaxy , luminosity , astronomy , active galactic nucleus , accretion (finance) , elliptical galaxy , surface brightness
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,tot ) , which is a measure of the galactic hot gas content, and their nuclear hard emission ( L HX,nuc ) , mostly coming from Chandra observations, which is a measure of the nuclear activity. At any optical luminosity, the highest L SX,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,tot (erg s −1 ) ≳ 41.5 cases. The highest L HX,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,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,nuc , even though the highest L HX,nuc are all associated with optical nuclei. The implications of these findings for galaxy evolution and accretion modalities at the present epoch are discussed.