... quasars

Figures 2 to 21, 23 to 25, 31 to 34 and Tables 3 to 16 are only available in electronic form at http://www.edpsciences.org

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...2004)

The reason why we did not use later releases (DR3 or DR4) is because, as discussed in the following, we had to inspect individually each spectrum to remove broad absorption line quasars, and DR2 has a number of objects for which this process is feasible.

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... quasars

We regard the SDSS spectroscopic targets as quasars when the objects are classified as "quasars'' (specClass=3) or "high-z quasars'' (specClass=4) by the SDSS classification algorithm.

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... IRAF

IRAF (Image Reduction and Analysis Facility) is distributed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy Inc., under corporative agreement with the National Science Foundation.

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