Spectral Classification of Quasars in the Sloan Digital Sky Survey: Eigenspectra, Redshift, and Luminosity Effects

By C. Yip, Andrew J. Connolly, D. V. vanden Berk, Zhaoming Ma, J. Frieman, Mark SubbaRao, A. Szalay, G. T. Richards, P. Hall, D. Schneider and 3 more. 2004

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We study 16,707 quasar spectra from the Sloan Digital Sky Survey (SDSS) (an early version of the First Data Release; DR1) using the Karhunen-Loève transform (or principal components analysis). The redshifts of these quasars range from 0.08 to 5.41, the i-band absolute magnitudes from -30 to -22, and the resulting rest-frame wavelengths from 900 to 8000 Å. The quasar eigenspectra of the full catalog reveal the following: first order—the mean spectrum; second order—a host-galaxy component; third order—the UV-optical continuum slope; fourth order—the correlations of Balmer emission lines. These four eigenspectra account for 82% of the total sample variance. Broad absorption features are found not to be confined in one particular order but to span a number of higher orders. We find that the spectral classification of quasars is redshift and luminosity dependent; as such there does not exist a compact set (i.e., less than ≈10 modes) of eigenspectra (covering 900–8000 Å) that can describe most variations (i.e., greater than ≈95%) of the entire catalog. We therefore construct several sets of eigenspectra in different redshift and luminosity bins. From these eigenspectra we find that quasar spectra can be classified (by the first two eigenspectra) into a sequence that is defined by a simple progression in the steepness of the slope of the continuum. We also find a dependence on redshift and luminosity in the eigencoefficients. The dominant redshift effect is a result of the evolution of the blended Fe II emission (optical) and the Balmer continuum (the "small bump," λrest ≈ 2000–4000 Å). A luminosity dependence is also present in the eigencoefficients and is related to the Baldwin effect—the decrease of the equivalent width of an emission line with luminosity, which is detected in Lyα, Si IV+O IV], C IV, He II, C III] and Mg II, while the effect in N V seems to be redshift dependent. If we restrict ourselves to the rest-wavelength regions 1150–2000 Å and 4000–5500 Å, the eigenspectra constructed from the wavelength-selected SDSS spectra are found to agree with the principal components by Francis et al. and the well-known "Eigenvector-1" of Boroson & Green, respectively. ASCII formatted tables of the eigenspectra are available.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies. I. Galaxy Mergers and Quasar Activity (2007, background): “…host galaxies reveal the presence of young stellar populations indicative of a recent starburst (Brotherton et al. 1999; Canalizo & Stockton 2001; Kauffmann et al. 2003; Yip et al. 2004; Jahnke et al. 2004a, 2004b; Sánchez et al. 2004; Vanden Berk et al. 2006; Barthel 2006; Zakamska et al. 2006).”
LOW-RESOLUTION SPECTRAL TEMPLATES FOR ACTIVE GALACTIC NUCLEI AND GALAXIES FROM 0.03 TO 30 μm (2010, background): “R E SO L U T IO N SPE C T R A L T E M PL A T E S FO R A G N s A N D G A L A X IE S 975 the SED on black hole (BH) mass and accretion rate (e.g., Yip et al. 2004).”
SDSS DR7 WHITE DWARF CATALOG (2012, methodology): “We removed the known quasars (Schneider et al. 2010), BL Lac objects (Plotkin et al. 2010), and once we had run through our DA and DB model-ﬁtting program, we ﬁt the rejects with galaxy and quasar templates (Yip et al. 2004a, 2004b) to remove these objects from further consideration.”
THINK OUTSIDE THE COLOR BOX: PROBABILISTIC TARGET SELECTION AND THE SDSS-XDQSO QUASAR TARGETING CATALOG (2010, background): “Although there are well-known correlations between quasar spectral properties and luminosity (e.g., Baldwin 1977; Yip et al. 2004), these trends are very subtle and they mostly affect emission line shapes.”
The Relation between Quasar and Merging Galaxy Luminosity Functions and the Merger-driven Star Formation History of the Universe (2006, background): “…of mergers (Stockton 1978; Heckman et al. 1984; Stockton & MacKenty 1987; Stockton & Ridgway 1991; Hutchings & Neff 1992; Bahcall et al. 1994, 1995, 1997; Canalizo & Stockton 2001) and starbursts (Brotherton et al. 1999, 2002; Canalizo et al. 2000; Yip et al. 2004; Vanden Berk et al. 2006).”
UNIFICATION OF LUMINOUS TYPE 1 QUASARS THROUGH C iv EMISSION (2010, background): “In addition, spectral PCA analyses (Francis et al. 1992; Shang et al. 2003; Yip et al. 2004) have identified other correlations between emission lines, broad absorption lines, and the continuum.”
Average extinction curves and relative abundances for quasi-stellar object absorption-line systems at 1 ≤zabs < 2 (2006, methodology): “The spectra (and associated error arrays) were normalized by reconstructions of the QSO continua, using the first 30 QSO eigenspectra derived by Yip et al. (2004).”
Soft X-Ray and Ultraviolet Emission Relations in Optically Selected AGN Samples (2005, methodology): “The host galaxy and AGN components were created using the first 3–20 galaxy and AGN eigenspectra obtained from large SDSS samples by Yip et al. (2004a, 2004b).”
The Sloan Digital Sky Survey quasar catalog: ninth data release (2012, methodology): “The technique to derive PCA components of quasar spectra has been described in detail in several papers (e.g. Franciset al. 1992; Yip et al. 2004; Suzuki et al. 2005).”
THE z = 5 QUASAR LUMINOSITY FUNCTION FROM SDSS STRIPE 82 (2012, methodology): “We apply the model at higher redshift under the assumption that the distribution of quasar SEDs does not evolve with redshift (Kuhn et al. 2001; Yip et al. 2004; Jiang et al. 2006).”
An Observational Determination of the Bolometric Quasar Luminosity Function (2006, result): “…contrary to the expectation from other observations of high-redshift optical quasar SEDs (Vanden Berk et al. 2001, 2005; Kuhn et al. 2001; Pentericci et al. 2003; Yip et al. 2004; Jiang et al. 2006b) and the observed highredshift DR3 quasar colors (e.g., Richards et al. 2001, 2006b; see also Fig.”