Composite Quasar Spectra from the Sloan Digital Sky Survey

By S. C. D. E. V. Berk, et al. 2001

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We have created a variety of composite quasar spectra using a homogeneous data set of over 2200 spectra from the Sloan Digital Sky Survey (SDSS). The quasar sample spans a redshift range of 0.044 ≤ z ≤ 4.789 and an absolute r' magnitude range of -18.0 to -26.5. The input spectra cover an observed wavelength range of 3800–9200 A at a resolution of 1800. The median composite covers a rest-wavelength range from 800 to 8555 A and reaches a peak signal-to-noise ratio of over 300 per 1 A resolution element in the rest frame. We have identified over 80 emission-line features in the spectrum. Emission-line shifts relative to nominal laboratory wavelengths are seen for many of the ionic species. Peak shifts of the broad permitted and semiforbidden lines are strongly correlated with ionization energy, as previously suggested, but we find that the narrow forbidden lines are also shifted by amounts that are strongly correlated with ionization energy. The magnitude of the forbidden line shifts is 100 km s-1, compared with shifts of up to 550 km s-1 for some of the permitted and semiforbidden lines. At wavelengths longer than the Lyα emission, the continuum of the geometric mean composite is well fitted by two power laws, with a break at ≈5000 A. The frequency power-law index, αν, is -0.44 from ≈1300 to 5000 A and -2.45 redward of ≈5000 A. The abrupt change in slope can be accounted for partly by host-galaxy contamination at low redshift. Stellar absorption lines, including higher order Balmer lines, seen in the composites suggest that young or intermediate-age stars make a significant contribution to the light of the host galaxies. Most of the spectrum is populated by blended emission lines, especially in the range 1500–3500 A, which can make the estimation of quasar continua highly uncertain unless large ranges in wavelength are observed. An electronic table of the median quasar template is available.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d49e90b04587b635befdac166f081bf34fd09b18

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Citations in the corpus

Spectral Classification of Quasars in the Sloan Digital Sky Survey: Eigenspectra, Redshift, and Luminosity Effects (2004, methodology): “This line-shift behavior was found in many other studies (see references in Vanden Berk et al. 2001).”
Fueling Low-Level AGN Activity through Stochastic Accretion of Cold Gas (2006, background): “Supp., 132, 86 Hasinger, G., Miyaji, T., & Schmidt, M. 2005, A&A, in press [astro-ph/0506118] Heckman, T. M., Bothun, G. D., Balick, B., & Smith, E. P. 1984,AJ, 89, 958 Heckman, T. M., Blitz, L., Wilson, A. S., Armus, L., & Miley, G. K. 1989, ApJ, 342, 735 Heckman, T. M., Kauffmann, G., Brinchmann, ”
Spectroscopic Target Selection in the Sloan Digital Sky Survey: The Quasar Sample (2002, background): “The overall shape of the featureless continua of quasars is well approximated by a power-law (Vanden Berk et al. 2001), although the continuum need not be a power-law physically.”
Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity (2008, background): “2003b, MNRAS, 339, 312 Srianand, R., & Khare, P. 1996, MNRAS, 280, 767 Stanway, E. R., McMahon, R. G., & Bunker, A. J. 2005, MNRAS, 359, 1184 Stark, D. P., Bunker, A. J., Ellis, R. S., Eyles, L. P., & Lacy, M. 2007a, ApJ, 659, 84 Stark, D. P., Ellis, R. S., Richard, J., Kneib, J.-P., Smith, G. P., &”
THE MULTI-OBJECT, FIBER-FED SPECTROGRAPHS FOR THE SLOAN DIGITAL SKY SURVEY AND THE BARYON OSCILLATION SPECTROSCOPIC SURVEY (2012, background): “2003, AJ, 125, 1559 Predehl, P., et al. 2010, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Vol. 7732 Ross, N. P., et al. 2012, ApJS, 199, 3 Schlegel, D., White, M., & Eisenstein, D. 2009, in astro2010: The Astronomy and Astrophysics Decadal Survey, arXiv:0902.4680,”
The Rest-Frame Extreme-Ultraviolet Spectral Properties of Quasi-stellar Objects (2001, methodology): “Vanden Berk et al. (2001) quote a power-law index in their median composite between Lya and 4000 equivalent to what weA , call of [0.46, signiÐcantly harder than our value ofaNUV,[0.71.”
The COMBO-17 survey: Evolution of the galaxy luminosity function from 25,000 galaxies with 0.2 < z < 1.2 (2002, methodology): “The quasar library has also been improved by deriving it from the more modern SDSS QSO template spectrum (vanden Berk 2001) rather than from the Francis et al. (1991) emission line contour.”
The Sloan Digital Sky Survey Quasar Catalog. II. First Data Release (2003, methodology): “A composite quasar spectrum formed from SDSS data is discussed by Vanden Berk et al. (2001).”
Universal bolometric corrections for active galactic nuclei over seven luminosity decades (2020, methodology): “(8) of Ross et al. (2013), then we converted them into 2500 Å fluxes using the standard method outlined in Richards et al. (2006), and finally converted into 4500 Å fluxes assuming a power-law SED Lν ∝ ν−α with α = 0.5 (Vanden Berk et al. 2001, check footnote 5).”
The Sloan Digital Sky Survey Quasar Catalog: Sixteenth Data Release (2020, methodology): “49 Specifically, Section 3.2, requirement 1, of Dawson et al. (2016). plotted here, the line rest wavelengths were taken from Table 2 of Vanden Berk et al. (2001).”
Towards a physical model of dust tori in Active Galactic Nuclei (2005, methodology): “For wavelengths longer than Lyman alpha, it includes data from 2200 quasars of the Sloan Digital Sky Survey (Vanden Berk et al. 2001), which results in a power law with a spectral index ofαν =−0.46 2.”
Local supermassive black holes, relics of active galactic nuclei and the X-ray background (2003, background): “In the opticalUV region our template consists of a broken power-law with α = −0.44 (Lν ∝ να) in the range 1µm < λ < 1300Å and α = −1.76 in the range 1200-500Å (e.g. Telfer et al. 2002; Vanden Berk et al. 2001).”
Black Hole Growth to z = 2 - I: Improved Virial Methods for Measuring M_BH and L/L_Edd (2012, methodology): “For sources atz > 1, we estimatedfν ( 4400Å ) using the continuum flux density near 2200Å and by assuming fν ∝ ν−0.44 (Vanden Berk et al. 2001, VdB01 hereafter).”
The UKIRT Infrared Deep Sky Survey ZY JHK photometric system: passbands and synthetic colours (2006, background): “High signal-to-noise ratio composite spectra from large quasar surveys (Francis et al. 1991; Brotherton et al. 2001; Vanden Berk et al. 2001) provide information for the wavelength range 1000 . λ .”
An Exploratory Chandra Survey of a Well-defined Sample of 35 Large Bright Quasar Survey Broad Absorption Line Quasars (2006, methodology): “For reference, we also examined the effects of calculating f2500 by extrapolating from observed-frame blue photometry by assuming a typical quasar ultraviolet continuum described by a power law with spectral index, αν = −0.44 (Vanden Berk et al. 2001).”