A Direct Upper Limit on the Density of Cosmological Dust from the Absence of an X‐Ray Scattering Halo around thez = 4.3 Quasar QSO 1508 \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $+$ \end{document} 5714

Abstract

We report on the results of a search for an intergalactic X-ray dust scattering halo in a deep observation of the bright, high-redshift quasar QSO 1508+5714 with the Chandra X-Ray Observatory. We do not detect such a halo. Our result implies an upper limit on the density of diffuse, large-grained intergalactic dust of Ωd < 2 × 10-6, assuming a characteristic grain size of ~1 μm. The result demonstrates the sensitivity of this technique for detecting very small amounts of intergalactic dust, which are very hard to detect otherwise. This will allow us to put important constraints on systematic effects induced by extinction on the interpretation of the Hubble diagram for Type Ia supernovae, as well as on the amount and properties of cosmological dust being expelled into the intergalactic medium at early (z ≥ 2) times.