X-ray spectral evolution of high redshift quasars

Jill Bechtold, Martin Elvis, Fabrizio Fiore, Olga Kuhn, Roc M. Cutri, Jonathan C. Mcdowell, Marcia Rieke, Aneta Siemiginowska, Belinda J. Wilkes

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


At z≈3, the x-ray spectra of radio-loud and radio-quiet quasars are different. High-redshift radio-quiet quasars either have large absorbing columns, NH, and steeper power law spectral indices, αE, than low redshift quasars, or no absorption and similar αE's. In contrast, the radio-loud quasars at high redshift have substantial absorption and similar αE's to low redshift quasars. Implications for the interpretation of the evolution of the luminosity function of quasars are discussed. If the absorption arises outside the central engine for both radio-loud and radio-quiet quasars, then radio-quiet quasars differ from the radio-loud quasars in that their emitted power law spectrum has evolved with redshift. We argue that this favors models where quasars are numerous and short-lived, rather than rare and long-lived.

Original languageEnglish (US)
Pages (from-to)759-765
Number of pages7
JournalAstronomical Journal
Issue number3
StatePublished - Sep 1994

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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