Abstract
THE first step in gleaning cosmological information from quasars is to determine their spatial distribution and luminosity function, based on well defined, complete samples1,2. This idealised situation applies to a great extent in the case of radio quasars. For the majority of quasars, which are radio quiet, however, existing samples based on ultraviolet excess are not only incomplete, but are dominated by colour selection effects3. The relative importance of these effects depends on redshift, and, in particular the detection of high redshift quasars is extremely difficult4; consequently other methods of selection of radio-quiet quasars and BL Lac-type objecrs have been suggested5,6. Here, one such method based on optical variability is considered, with particular regard to a sample of 13 objects observed by van den Bergh et al. (BHP)6.
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SANITT, N. Selection of quasars by variability. Nature 258, 586–587 (1975). https://doi.org/10.1038/258586a0
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DOI: https://doi.org/10.1038/258586a0
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