First observation of a quasar with a redshift of 4

TLDR: In this paper, the authors reported the discovery of a quasar (0046- 293) with a redshift z = 4.01 and another (0044-276) with redshift Z = 3.42.

Abstract: 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 quasars1,2 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 (mR>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.