Intergalactic Dust and Observations of Type Ia Supernovae
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Abstract
Estimates of the cosmic star formation rate and of cluster metallicities independently imply that at z 0 of this must be destroyed in the IGM or during the ejection process. Assuming the Draine & Lee dust model and preferential destruction of small grains, I calculate the reddening and extinction of a uniform cosmological dust component in terms of (f) and the minimum grain size a_min. Very small grains provide most of the reddening but less than half of the opacity for optical extinction. For f > 0.3 and a_min > 0.1 microns, the intergalactic dust would be too grey to have been detected by its reddening, yet dense enough to be cosmologically important: it could account for the recently observed type Ia supernova dimming at z ~ 0.5 without cosmic acceleration. The importance of grey intergalactic dust of the described type can be tested by observations of z=0.5 supernovae in (rest) R-band or longer wavelengths and by the fluxes of a large sample of supernovae at z > 1. (Abridged)