Showing papers by "Mike Irwin published in 1987"
TL;DR: 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.
64 citations
TL;DR: The detection of high-redshift quasars (z > 3) offers the most direct method for studying conditions in the Universe at early epochs, while detailed observations of the quasar spectra provide information on the properties and evolution of intervening absorption systems such as the Lyman-α clouds as discussed by the authors.
Abstract: The detection of high-redshift quasars (z > 3) offers the most direct method for studying conditions in the Universe at early epochs. Analysis of the changes in the luminosity function of the quasar population places constraints on the epoch of formation of massive, gravitationally bound systems, while detailed observations of the quasar spectra provide information on the properties and evolution of intervening absorption systems such as the Lyman-α clouds. We report here the discovery of two new quasars of very high redshift; Q0051 – 279 of z=4.43 and Q0101 – 304 of z=4.07. These two quasars bring to five the total number of quasars known with z>4 (refs 1–3). The redshift of Q0051 – 279 is the highest yet recorded and compares with the z =4.11 of the previous most distant known quasar3. Both new quasars were found by the same multicolour technique and in the same UK-Schmidt-Telescope (UKST) field as Q0046–293, the first quasar found with a redshift z>4 (ref. 1). The multicolour selection technique, coupled with other quantitative searches now in progress, provides the means for deriving a greatly improved description of quasar evolution at high redshifts.
18 citations
13 citations
TL;DR: Techniques for analysing very large numbers of low-resolution optical spectra obtained through measurements of wide field photographic plates by fast microdensitometers are described, and the main characteristics of the data are outlined.
2 citations
01 Jan 1987
TL;DR: In this article, the application of technigues which utilise all the information contained in multi-colour surveys of stellar-like objects can be employed to detect guasars over an extended redshift range.
Abstract: We describe how the application of technigues which utilise all the information contained in multi-colour surveys of stellar-like objects can be employed to detect guasars over an extended redshift range. The method is particularly effective for the identification of guasars with redshifts z>2.2 where the application of the ultra-violet excess criterion breaks down. Spectroscopy of a small sample of objects from the first survey field has resulted in the detection of two new faint guasars with redshifts z=3.42 and z=4.01 (ref. 1).