Composite Quasar Spectra from the Sloan Digital Sky Survey

doi:10.1086/321167

The Astronomical Journal

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The Astronomical Journal Volume 122 Number 2 Create an alert RSS this journal

Daniel E. Vanden Berk et al. 2001 The Astronomical Journal 122 549 doi:10.1086/321167

Composite Quasar Spectra from the Sloan Digital Sky Survey^*

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Daniel E. Vanden Berk¹, Gordon T. Richards², Amanda Bauer³, Michael A. Strauss⁴, Donald P. Schneider², Timothy M. Heckman⁵, Donald G. York^6,7, Patrick B. Hall^4,8, Xiaohui Fan^4,9, G. R. Knapp⁴, Scott F. Anderson¹⁰, James Annis¹, Neta A. Bahcall⁴, Mariangela Bernardi⁶, John W. Briggs⁶, J. Brinkmann¹¹, Robert Brunner¹², Scott Burles¹, Larry Carey¹⁰, Francisco J. Castander^6,13, A. J. Connolly¹⁴, J. H. Crocker⁵, István Csabai^5,15, Mamoru Doi¹⁶, Douglas Finkbeiner¹⁷, Scott Friedman⁵, Joshua A. Frieman^1,6, Masataka Fukugita¹⁸, James E. Gunn⁴, G. S. Hennessy¹⁹, Željko Ivezić⁴, Stephen Kent^1,6, Peter Z. Kunszt⁵, D. Q. Lamb⁶, R. French Leger¹⁰, Daniel C. Long¹¹, Jon Loveday²⁰, Robert H. Lupton⁴, Avery Meiksin²¹, Aronne Merelli^11,22, Jeffrey A. Munn²³, Heidi Jo Newberg²⁴, Matt Newcomb²², R. C. Nichol²², Russell Owen¹⁰, Jeffrey R. Pier²³, Adrian Pope^5,22, Constance M. Rockosi⁶, David J. Schlegel⁴, Walter A. Siegmund¹⁰, Stephen Smee^5,25, Yehuda Snir²², Chris Stoughton¹, Christopher Stubbs¹⁰, Mark SubbaRao⁶, Alexander S. Szalay⁵, Gyula P. Szokoly⁵, Christy Tremonti⁵, Alan Uomoto⁵, Patrick Waddell¹⁰, Brian Yanny¹ and Wei Zheng⁵

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¹ Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510
² Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802
³ Department of Physics, University of Cincinnati, Cincinnati, OH 45221
⁴ Princeton University Observatory, Peyton Hall, Princeton, NJ 08544-1001
⁵ Department of Physics and Astronomy, Johns Hopkins University, 3701 San Martin Drive, Baltimore, MD 21218
⁶ Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637
⁷ Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637
⁸ Pontificia Universidad Católica de Chile, Departamento de Astronomía y Astrofísica, Facultad de Física, Casilla 306, Santiago 22, Chile
⁹ Institute for Advanced Study, Olden Lane, Princeton, NJ 08540-0631
¹⁰ Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195
¹¹ Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059
¹² Department of Astronomy, 105-24, California Institute of Technology, 1201 East California Boulevard, Pasadena, CA 91125
¹³ Observatoire Midi-Pyréneés, 14 Avenue Edouard Belin, F-31400 Toulouse, France
¹⁴ Department of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, PA 15260
¹⁵ Department of Physics of Complex Systems, Eötvös University, Pázmány Péter sétány 1/A, H-1117 Budapest, Hungary
¹⁶ Department of Astronomy and Research Center for the Early Universe, School of Science, University of Tokyo, Hongo, Bunkyo, Tokyo, 113-0033, Japan
¹⁷ Departments of Physics and Astronomy, University of California, Berkeley, 601 Campbell Hall, Berkeley, CA 94720
¹⁸ Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, 2778582, Japan
¹⁹ US Naval Observatory, 3450 Massachusetts Avenue, NW, Washington, DC 20392-5420
²⁰ Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QJ, UK
²¹ Royal Observatory, Edinburgh, EH9 3HJ, UK
²² Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15232
²³ US Naval Observatory, Flagstaff Station, P.O. Box 1149, Flagstaff, AZ 86002-1149
²⁴ Department of Physics, Rensselaer Polytechnic Institute, SC1C25, Troy, NY 12180
²⁵ Department of Astronomy, University of Maryland, College Park, MD 20742-2421

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Abstract References Cited By

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 Å at a resolution of 1800. The median composite covers a rest-wavelength range from 800 to 8555 Å and reaches a peak signal-to-noise ratio of over 300 per 1 Å 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 lesssim 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 Å. The frequency power-law index, α_ν, is -0.44 from ≈1300 to 5000 Å and -2.45 redward of ≈5000 Å. 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 Å, 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.

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Composite Quasar Spectra from the Sloan Digital Sky Survey^*