The Sloan Digital Sky Survey Quasar Catalog. 4. Fifth Data Release Page: 3 of 37
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the designation of a given source can change between data releases. Except on very rare occasions (see 5.1),
this change in position is much less than 1". When merging SDSS Quasar Catalogs with previous databases
one should always use the coordinates, not object names, to identify unique entries.
The DR5 catalog does not include classes of Active Galactic Nuclei (AGN) such as Type 2 quasars,
Seyfert galaxies, and BL Lacertae objects; studies of these sources in the SDSS can be found in Zakamska et
al. (2003) (Type 2), Kauffmann et al. (2003) and Hao et al. (2005) (Seyferts), and Collinge et al. (2005) and
Anderson et al. (2007) (BL Lacs). Spectra of the highest redshift SDSS quasars (z > 5.7; e.g., Fan et al. 2003,
2006a) were not acquired as part of the SDSS quasar survey (the objects were identified as candidates in
the SDSS imaging data, but the spectra were not obtained with the SDSS spectrographs), so they are not
included in the catalog.
The observations used to produce the catalog are presented in Section 2; the construction of the catalog
and the catalog format are discussed in Sections 3 and 4, respectively. Section 5 presents an overview of the
catalog, and a summary is given in Section 6. The catalog is presented in an electronic table in this paper
and can also be found at an SDSS public web site.1
2.1. Sloan Digital Sky Survey
The Sloan Digital Sky Survey uses a CCD camera (Gunn et al. 1998) on a dedicated 2.5-m telescope
(Gunn et al. 2006) at Apache Point Observatory, New Mexico, to obtain images in five broad optical bands
(ugriz; Fukugita et al. 1996) over approximately 10,000 deg2 of the high Galactic latitude sky. The sur-
vey data-processing software measures the properties of each detected object in the imaging data in all
five bands, and determines and applies both astrometric and photometric calibrations (Pier et al., 2003;
Lupton et al. 2001; Ivezit et al. 2004). Photometric calibration is provided by simultaneous observations
with a 20-inch telescope at the same site (see Hogg et al. 2001, Smith et al. 2002, Stoughton et al. 2002, and
Tucker et al. 2006). The SDSS photometric system is based on the AB magnitude scale (Oke & Gunn 1983).
The catalog contains photometry from 204 SDSS imaging runs acquired between 19 September 1998
(Run 94) and 13 May 2005 (Run 5326).
2.2. Target Selection
The SDSS filter system was designed to identify quasars at redshifts between zero and approximately
six; most quasar candidates are selected based on their location in multidimensional SDSS color-space. The
Point Spread Function (PSF) magnitudes are used for the quasar target selection, and the selection is based
on magnitudes and colors that have been corrected for Galactic extinction (using the maps of Schlegel,
Finkbeiner, & Davis 1998). An i magnitude limit of 19.1 is imposed for candidates whose colors indicate a
probable redshift of less than , 3.0 (selected from the ugri color cube); high-redshift candidates (selected from
the griz color cube) are accepted if i < 20.2 and the source is unresolved. The errors on the i measurements
are typically 0.02 0.03 and 0.03 0.04 magnitudes at the brighter and fainter limits, respectively. In addition
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Schneider, Donald P.; Hall, Patrick B.; Richards, Gordon T.; Strauss, Michael A.; Vanden Berk, Daniel E.; Anderson, Scott F. et al. The Sloan Digital Sky Survey Quasar Catalog. 4. Fifth Data Release, article, April 1, 2007; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc888372/m1/3/: accessed January 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.