Upper Limit on Dimming of Cosmological Sources by Intergalactic Grey Dust from the Soft X-ray Background

TL;DR

This paper constrains the amount of intergalactic grey dust by analyzing the soft X-ray background and diffuse halos around AGN, limiting dust opacity and aiding future cosmological measurements.

Contribution

It provides new upper limits on intergalactic dust opacity using X-ray background data and halo observations, reducing uncertainties in dark energy studies.

Findings

Intergalactic dust opacity limited to tau_GD<0.15 at z~1

Diffuse X-ray halos around AGN are less than 10% of the SXB

Constraints are weakly dependent on dust grain size and evolution

Abstract

Active Galactic Nuclei (AGN) produce a dominant fraction (~80%) 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 halos around AGN. Taking account of known galaxies and galaxy clusters, only a fraction F_halo <10% of the SXB can be in the form of diffuse X-ray halos 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 mum) to a level tau_GD<0.15(F_halo/10%) to a redshift z~1. Our results are only weakly dependent on the grain size distribution 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.