Spectral energy distributions and multiwavelength selection of type 1 quasars

Gordon T. Richards, Mark Lacy, Lisa J. Storrie-Lombardi, Patrick B. Hall, S. C. Gallagher, Dean C. Hines, Fan Xiaohui, Casey Papovich, Daniel E. Vanden Berk, George B. Trammell, Donald P. Schneider, Marianne Vestergaard, Donald G. York, Sebastian Jester, Scott F. Anderson, Tamás Budavári, Alexander S. Szalay

Research output: Contribution to journalArticlepeer-review

909 Scopus citations


We present an analysis of the mid-infrared (MIR) and optical properties of type 1 (broad-line) quasars detected by the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z ∼ 3, with predictions to z = 7. We demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei (AGNs) than MIR or optical colors alone. Composite spectral energy distributions (SEDs) are constructed for 259 quasars with both Sloan Digital Sky Survey and Spitzer photometry, supplemented by near-IR, GALEX, VLA, and ROSAT date, where available. We discuss how the spectral diversity of quasars influences the determination of bolometric luminosities and accretion rates; assuming the mean SED can lead to errors as large as 50% for individual quasars when inferring a bolometric luminosity from an optical luminosity. Finally, we show that careful consideration of the shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened / obscured AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio.

Original languageEnglish (US)
Pages (from-to)470-497
Number of pages28
JournalAstrophysical Journal, Supplement Series
Issue number2
StatePublished - Oct 2006

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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