A complete sample of quasars at B = 19.80

A multicolor optical survey of QSOs to B of about 21.8 in the Hercules field

“…The averages, along with results from other surveys shown in the same figure (note, in particular, the excellent agreement of our results with those of an independent but similar 4-m photographic multicolor survey by Maraño et al 1988), clearly indicate a flattening in the slope of the integrated counts of QSOs at faint magnitudes relative to that at bright magnitudes. This feature alone can be used to exclude some QSO evolution models (KK; Schmidt and Green 1983;KKC;Marshall et al 1984;etc.). was based.…”

Schmidt Telescopes and Quasar Surveys

“…The use of very low dispersion objective prisms on Schmidt telescopes by Smith (1975), MacAlpine and others (1977) in the late 1970s led to the generation of the first large samples of what were then "high-redshift" quasars with z > 2. The work of Formiggini and collaborators (1980) based on Palomar UBV plate material produced one of the first optical samples of Marshall et al (1984) led to the recognition that the evolution of the quasar population for redshifts z < 2 could be represented by a very simple parameterisation in which the luminosity function retained its shape but the characteristic luminosity increased at higher redshift; the so-called pure-luminosity-evolution. At the very brightest magnitudes, TUB < 16, Schmidt and Green employed the Palomar 18-inch Schmidt to undertake the Palomar-Green ultraviolet excess survey (Green, Schmidt & Leibert 1986), a mammoth undertaking that denned our knowledge of the bright, low-redshift, quasar population for more than a decade.…”

“…The luminosity function has a characteristic luminosity, L*, at the point where the rate of increase in number as a function of decreasing luminosity becomes much shallower, N <x L~1 5 . Marshall et al (1984), and later Boyle et al (1987) using much improved data, showed that the evolution of the quasar luminosity function over the redshift range 0.3 £ z £ 2 could be represented by a luminosity function whose shape is invariant but whose characteristic luminosity changes with redshift according to the simple power-law form L* oc (1 + z) 3A . Particularly striking features of this result are the simplicity of the representation, and the strength of the evolution; the characteristic luminosity increases by a factor ~ 40 over the redshift range 0 < z < 2.…”

The Clustering and Evolution of QSOs

“…Unfortunately, whilst conventional spectroscopic techniques limited surveys to B < 20 mag, the derived LF exhibited a featureless power law form (Schmidt and Green 1983;Mitchell et al 1984;Marshall et al 1984) as represented by Fig. 1 a, and consequently little discrimination between evolutionary models was possible.…”

“…Until recently the prohibitive amounts of telescope time required to obtain spectroscopic confirmation for large numbers of faint QSO candidates had limited suitable QSO surveys to B < 20 mag and z < 2.2 (e.g. Schmidt and Green 1983;Marshall et al 1984). At these 'bright' magnitudes little discrimination was afforded between competing models for QSO evolution (see below) and the space density of QSOs was too low to conduct a detailed analysis of their clustering properties at scales less than 50 h-1 Mpc (Osmer 1981).…”