Candidate type II quasars from the Sloan Digital Sky Survey. II. From radio to X-rays

Nadia L. Zakamska, Michael A. Strauss, Timothy M. Heckman, Željko Ivezić, Julian H. Krolik

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95 Scopus citations


Type II quasars are luminous active galactic nuclei (AGNs) whose central engines and broad-line regions are obscured by intervening material; such objects only recently have been discovered in appreciable numbers. We study the multiwavelength properties of 291 type II AGN candidates (0.3 < z < 0.8) selected on the basis of their optical emission-line properties from the spectroscopic database of the Sloan Digital Sky Survey. This sample includes about 150 objects luminous enough to be classified as type II quasars. We matched the sample to the FIRST (20 cm), IRAS (12-100 μm), 2MASS (JHK S), and RASS (0.1-2.4 keV) surveys. Roughly 10% of optically selected type II AGN candidates are radio-loud, comparable to the AGN population as a whole. About 40 objects are detected by IRAS at 60 and/or 100 μm, and the inferred mid/far-IR luminosities lie in the range νLν = 10 45-3 × 1046 ergs s-1. Average IR-to-[O III] λ5007 ratios of objects in our sample are consistent with those of other AGNs. Objects from our sample are 10 times less likely to have soft X-ray counterparts in RASS than type I AGNs with the same redshifts and [O III] λ5007 luminosities. The few type II AGN candidates from our sample that are detected by RASS have harder X-ray spectra than those of type I AGNs. The multiwavelength properties of the type II AGN candidates from our sample are consistent with their interpretation as powerful obscured AGNs.

Original languageEnglish (US)
Pages (from-to)1002-1016
Number of pages15
JournalAstronomical Journal
Issue number3 1785
StatePublished - Sep 2004

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: active
  • Infrared: galaxies
  • Quasars: general
  • Surveys
  • X-rays: galaxies


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