Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.1110f&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #11.10; Bulletin of the American Astronomical Society, Vol. 24, p.1135
Astronomy and Astrophysics
Astronomy
Scientific paper
The Large Bright QSO Survey (LBQS) is the largest extant uniform sample of optically-selected QSOs. Candidates were chosen from magnitude-limited samples using objectively-defined selection criteria applied to digitized objective-prism spectra. The survey consists of positions, apparent magnitudes, and spectra of more than 1000 QSOs brighter than B_J =~ 18.9. Fewer than 1% of the candidates remain unidentified. We have analyzed a sample of 1049 QSOs and AGN from the LBQS to produce a new estimate of the shape and the evolutionary behavior of the luminous end of the QSO luminosity function. These data represent more than an order of magnitude improvement in the determination of the space density of QSOs in the redshift range 0.2 < z < 3, with absolute magnitudes corresponding to apparent magnitudes in the range 16.5 < mB_J < 18.85. The results of this study can be summarized as follows: 1. The data are poorly described by the canonical model in which a two power-law luminosity function of constant shape evolves strongly until redshift ~ 2, in such a way as to mimic pure luminosity evolution. Relative to this model we find a higher space density of luminous QSOs at low redshift. 2. The shape of the luminosity function is not invariant with redshift, becoming steeper at higher redshift. 3. Compared to current models, the rate of evolution is less rapid over the redshift range 0.2 < z < 3, but continues, albeit at a reduced rate, until at least redshift ~ 3. The LBQS results may mitigate the theoretical problem of why the space density of QSOs undergoes such a dramatic change with cosmic time. Specifically, decreasing the rate of evolution while increasing the redshift out to which evolution extends has the effect of broadening the peak in space density, or equivalently, slowing the rate of change of the space density of QSOs with cosmic time. This work was supported by NSF grant AST 90-01181.
Chaffee Frederic H.
Foltz Craig B.
Hewett Paul C.
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