The evolution of optically selected QSOs

Astronomy and Astrophysics – Astronomy

Scientific paper

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Galactic Evolution, Quasars, Astronomical Catalogs, Luminosity, Magnitude, Red Shift

Scientific paper

A determination of the QSO luminosity function and its evolution with redshift is reported based on a new catalog of faint UV-excess (UVX) QSOs with complete spectroscopic identification for almost 200 QSOs by Boyle et al. It is found that the steep slope (d log N/dB of about 0.86) exhibited by the number-magnitude relation for UVX QSOs flattens significantly (d log N/dB of about 0.32) beyond B = 19.5 mag, with a UVX QSO surface density at B of less than 20.9 mag of 36 + or - 4/sq deg. It is demonstrated that this flattening corresponds to a feature in the QSO luminosity function at faint absolute magnitudes. By determining the redshift dependence of this feature it is found that the evolution of QSOs at z of less than 2.2 is most simply parameterized by a uniform increase in their luminosity with increasing redshift. Such evolution is found to be consistent with a model in which QSOs are long-lived, gradually dimming in luminosity from their epoch of formation at z of greater than 2.2 to the present day.

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