A catalogue and analysis of X-ray luminosities of early-type galaxies

We present a catalogue of X-ray luminosities for 401 early-type galaxies, of which 136 are based on newly analysed ROSAT PSPC pointed observations. The remaining luminosities are taken from the literature and converted to a common energy band, spectral model and distance scale. Using this sample we fit the L-X: L-B relation for early-type galaxies and find a best-fit slope for the catalogue of similar to2.2. We demonstrate the influence of group-dominant galaxies on the fit and present evidence that the relation is not well modelled by a single power-law fit. We also derive estimates of the contribution to galaxy X-ray luminosities from discrete-sources and conclude that they provide L-dscr/L-B similar or equal to 29.5 erg s L-B.(-1). We compare this result with luminosities from our catalogue. Lastly, we examine the influence of environment on galaxy X-ray luminosity and on the form of the L-X : L-B relation. We conclude that although environment undoubtedly affects the X-ray properties of individual galaxies, particularly those in the centres of groups and clusters, it does not change the nature of whole populations.