SIMBAD references

Scattering and absorption of light by a homogeneous distribution of intergalactic large dust grains has been proposed as an alternative, non-cosmological explanation for the faintness of type Ia supernovae at z∼0.5. We investigate the differential extinction for high-redshift sources caused by extragalactic dust along the line of sight. Future observations of type Ia supernovae up to z∼2, e.g. by the proposed SNAP satellite, will allow the measurement of the properties of dust over cosmological distances. We show that 1% relative spectrophotometric accuracy (or broadband photometry) in the wavelength interval 0.7-1.5µm is required to measure the extinction caused by ``grey'' dust down to δm=0.02mag. We also argue that the presence of grey dust is not necessarily inconsistent with the recent measurement of the brightness of a supernova at z=1.7 (SN 1997ff), in the absence of accurate spectrophotometric information of the supernova.