Upper limit on dimming of cosmological sources by intergalactic grey dust from the soft X-ray background |
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| Authors: | Mark Dijkstra Abraham Loeb |
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| Institution: | Institute for Theory &Computation, Harvard University, 60 Garden Street, Cambridge, MA 02138, USA |
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| Abstract: | Active galactic nuclei (AGN) produce a dominant fraction ( F AGN～ 80 per cent) of the soft X-ray background (SXB) at photon energies 0.5 < E < 2 keV . If dust pervaded throughout the intergalactic medium, its scattering opacity would have produced diffuse X-ray haloes around AGN. Taking account of known galaxies and galaxy clusters, only a fraction F halo? 10 per cent of the SXB can be in the form of diffuse X-ray haloes around AGN. We therefore limit the intergalactic opacity to optical/infrared photons from large dust grains, with radii in the range a = 0.2–2.0 μm , to a level τGD? 0.15( F halo/10 per cent)(FAGN/80 per cent)?1 to a redshift z ～ 1 . Our results are only weakly dependent on the grain size distribution in this size range or the redshift evolution of the intergalactic dust. Stacking X-ray images of AGN can be used to improve our constraints and diminish the importance of dust as a source of systematic uncertainty for future supernova surveys which aim to improve the precision on measuring the redshift evolution of the dark energy equation-of-state. |
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| Keywords: | scattering dust extinction intergalactic medium quasars: general cosmology: theory X-rays: diffuse background |
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