Nature 325, 131 - 133 (08 January 1987); doi:10.1038/325131a0

First observation of a quasar with a redshift of 4

S. J. Warren, P. C. Hewett, M. J. Irwin, R. G. McMahon, M. T. Bridgeland, P. S. Bunclark & E. J. Kibblewhite^*

Institute of Astronomy, Madingley Road, Cambridge CB3 OHA, UK
^*Present address: National Optical Astronomy Observatories, University of Arizona, Tucson, Arizona 85726, USA.

Quasars of high redshift (here z > 3.3) are the most distant objects known and provide direct information on the early Universe. However, only a few high-redshift quasars have been discovered and their detection remains problematic. We report here the discovery of a quasar (0046 – 293) with a redshift z = 4.01 and another (0044–276) with a redshift z =3.42. The redshift of the former quasar is the highest yet detected and compares with the z = 3.80 of the previous most distant known quasar¹. The new quasars lie in the same field as three other known high-redshift quasars^1,2 and were identified in a preliminary analysis of new multi-colour data derived from measurements of direct photographic plates taken with the United Kingdom Schmidt Telescope (UKST). The two new quasars are significantly fainter (m _R>19) than previously known high-redshift quasars discovered by optical techniques, and demonstrate that the luminosity function of optically selected high-redshift quasars extends over at least two magnitudes.

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