Dust-scattered X-ray halos are tracers not only of the physical properties of the scattering grains but also of their spatial distribution along the line of sight toward the X-ray source. Here I consider the case that an X-ray—bright quasar is seen through a dusty spiral galaxy. Based on the example of the QSO-galaxy association Mrk 205—NGC 4319, I point out that within the framework of Arp et al.'s Doppler interpretation of the redshifts of quasars it is possible that such quasars are surrounded by very weak X-ray halos, whereas no halos occur if the quasars are at cosmological distances. Critical remarks on the practical realization of this test conclude the paper.
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