A quasar-galaxy mixing diagram: Quasar spectral energy distribution shapes in the optical to near-infrared

Heng Hao, Martin Elvis, Angela Bongiorno, Gianni Zamorani, Andrea Merloni, Brandon C. Kelly, Francesca Civano, Annalisa Celotti, Luis C. Ho, Knud Jahnke, Andrea Comastri, Jonathan R. Trump, Vincenzo Mainieri, Mara Salvato, Marcella Brusa, Chris D. Impey, Anton M. Koekemoer, Giorgio Lanzuisi, Cristian Vignali, John D. SilvermanC. Megan Urry, Kevin Schawinski

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


We define a quasar-galaxy mixing diagram using the slopes of their spectral energy distributions (SEDs) from 1 μm to 3000 å and from 1 to 3 μm in the rest frame. The mixing diagram can easily distinguish among quasar-dominated, galaxy-dominated and reddening-dominated SED shapes. By studying the position of the 413 XMM-selected type 1 AGN in the wide-field 'Cosmic Evolution Survey' in the mixing diagram, we find that a combination of the Elvis et al. mean quasar SED with various contributions from galaxy emission and some dust reddening is remarkably effective in describing the SED shape from 0.3 to 3μm for large ranges of redshift, luminosity, black hole mass and Eddington ratio of type 1 AGN. In particular, the location in the mixing diagram of the highest luminosity AGN is very close (within 1σ) to that of the Elvis et al. SED template. The mixing diagram can also be used to estimate the host galaxy fraction and reddening in quasar. We also show examples of some outliers which might be AGN in different evolutionary stages compared to the majority of AGN in the quasar-host galaxy co-evolution cycle.

Original languageEnglish (US)
Pages (from-to)3104-3121
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Oct 2013


  • Galaxies: evolution
  • Quasars: general
  • Surveys

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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