Faint galaxies and the X-ray background
O. Almaini, T. Shanks, B. J. Boyle, I. Georgantopoulos, R. E. Griffiths, G. C. Stewart, K. F. Gunn, A. J. Blair
Abstract
We summarise our recent work on the faint galaxy contribution to the cosmic X-ray background (XRB). At bright X-ray fluxes (in the ROSAT pass band), broad line QSOs dominate the X-ray source population, but at fainter fluxes there is evidence for a significant contribution from emission-line galaxies. Here we present statistical evidence that these galaxies can account for a large fraction of the XRB. We also demonstrate that these galaxies have significantly harder X-ray spectra than QSOs. Finally we present preliminary findings from infra-red spectroscopy on the nature of this X-ray emitting galaxy population. We conclude that a hybrid explanation consisting of obscured/Type 2 AGN surrounded by starburst activity can explain the properties of these galaxies and perhaps the origin of the entire XRB.
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