Cosmological X-ray Scattering from Intergalactic Dust

Abstract

High resolution X-ray imaging offers a unique opportunity to probe the nature of dust in the z ~< 2 universe. Dust grains 0.1- 1 um in size will scatter soft X-rays, producing a diffuse "halo" image around an X-ray point source, with a brightness ~ few % confined to an arcminute-sized region. We derive the formulae for scattering in a cosmological context and calculate the surface brightness of the scattering halo due to (i) an IGM uniformly enriched (Omega_ d ~ 10^-5) by a power-law distribution of grain sizes, and (ii) a DLA-type (N_H ~ 10^21 cm^-2) dust screen at cosmological distances. The morphology of the surface brightness profile can distinguish between the two scenarios above, place size constraints on dusty clumps, and constrain the homogeneity of the IGM. Thus X-ray scattering can gauge the relative contribution of the first stars, dwarf galaxies, and galactic outflows to the cosmic metallicity budget and cosmic history of dust. We show that, because the amount of intergalactic scattering is overestimated for photon energies < 1 keV, the non-detection of an X-ray scattering halo by Petric et al. (2006) is consistent with `grey' intergalactic dust grains (Omega_d ~ 10^-5$) when the data is restricted to the 1-8 keV band. We also calculate the systematic offset in magnitude, delta m ~ 0.01, for such a population of graphite grains, which would affect the type of supernova survey ideal for measuring dark energy parameters within ~ 1% precision.

Published in ApJ, figures updated to published version

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Cited by in corpus (7)

• Dust Formation in Milky Way-like Galaxies
• The dust scattering component of X-ray extinction: Effects on continuum fitting and high-resolution absorption edge structure
• Interstellar Extinction
• A framework for the next generation of stationary cosmological models
• X-ray Scattering Echoes and Ghost Halos from the Intergalactic Medium: Relation to the nature of AGN variability
• Combined constraints on intergalactic dust from quasar colours and the soft X-ray background
• The X-ray variable sky as seen by MAXI: the future of dust echo tomography with bright Galactic X-ray bursts