Spectral evolution in high redshift quasars from the final Baryon Oscillation Spectroscopic Survey sample

Trey W. Jensen, M. Vivek, Kyle S. Dawson, Scott F. Anderson, Julian Bautista, Dmitry Bizyaev, William N. Brandt, Joel R. Brownstein, Paul Green, David W. Harris, Vikrant Kamble, Ian D. McGreer, Andrea Merloni, Adam Myers, Daniel Oravetz, Kaike Pan, Isabelle Pâris, Donald P. Schneider, Audrey Simmons, Nao Suzuki

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We report on the diversity in quasar spectra from the Baryon Oscillation Spectroscopic Survey. After filtering the spectra to mitigate selection effects and Malmquist bias associated with a nearly flux-limited sample, we create high signal-to-noise ratio composite spectra from 58,656 quasars (2.1 ≤ z ≤ 3.5), binned by luminosity, spectral index, and redshift. With these composite spectra, we confirm the traditional Baldwin effect (BE, i.e., the anticorrelation of C IV equivalent width (EW) and luminosity) that follows the relation Wλ ∝ Lβw with slope βw = -0.35 ± 0.004, -0.35 ± 0.005, and -0.41 ± 0.005 for z = 2.25, 2.46, and 2.84, respectively. In addition to the redshift evolution in the slope of the BE, we find redshift evolution in average quasar spectral features at fixed luminosity. The spectroscopic signature of the redshift evolution is correlated at 98% with the signature of varying luminosity, indicating that they arise from the same physical mechanism. At a fixed luminosity, the average C IV FWHM decreases with increasing redshift and is anti-correlated with C IV EW. The spectroscopic signature associated with C IV FWHM suggests that the trends in luminosity and redshift are likely caused by a superposition of effects that are related to black hole mass and Eddington ratio. The redshift evolution is the consequence of a changing balance between these two quantities as quasars evolve toward a population with lower typical accretion rates at a given black hole mass.

Original languageEnglish
Article number199
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 19 Dec 2016


  • black hole physics
  • galaxies: active
  • quasars: emission lines
  • quasars: general
  • surveys


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