IUE observations of the quasar 3C263 constrain the ionizing photon luminosity of decaying dark matter.

Abstract

Dark matter which produces hydrogen-ionizing photons on a time-scale of 2x10²³s has been shown by Sciama to explain many problems in astronomy and cosmology. Clusters of galaxies composed of such dark matter will be luminous sources of ionizing photons. The authors report here the results of a search for an otherwise unidentified, extended emission-line in the IUE spectrum of the quasar 3C 263. Optical imaging and spectroscopy of the quasar show that it lies at the centre of a moderately rich cluster of galaxies. No line was detected. Either the central surface density of dark matter in the cluster is less than 0.34 g cm^-2 or the decay lifetime of the dark matter exceeds the above estimate. Alternatively, the line may be absorbed by cold clouds similar to those recently discovered with X-ray spectra of nearby clusters.