The deep groth strip survey. VI. Spectroscopic, variability, and x-ray detection of active galactic nuclei

Vicki L. Sarajedini, David C. Koo, Andrew C. Phillips, Henry A. Kobulnicky, Karl Gebhardt, Christopher N.A. Willmer, Nicole P. Vogt, Elise Laird, Myungshin Im, Sarah Iverson, Wanessa Mattos

Research output: Contribution to journalReview articlepeer-review

30 Scopus citations


We identify active galactic nuclei (AGNs) in the Groth-Westphal Survey Strip (GSS) using the independent and complementary selection techniques of optical spectroscopy and photometric variability. We discuss the X-ray properties of these AGNs using ChandralXMM-Newton data for this region. From a sample of 576 galaxies with high-quality spectra we identify 31 galaxies with AGN signatures. Seven of these have broad emission lines (Type 1 AGNs). We also identify 26 galaxies displaying nuclear variability in Hubble Space Telescope Wide Field Planetary Camera 2 (HST WFPC2) images of the GSS separated by ∼7 yr. The primary overlap of the two selected AGN samples is the set of broad-line AGNs, of which 80% appear as variable. Only a few narrow-line AGNs approach the variability threshold. The broad-line AGNs have an average redshift of 〈z〉 ≃ 1.1, while the other spectroscopic AGNs have redshifts closer to the mean of the general galaxy population (〈z〉 ≃ 0.7). Eighty percent of the identified broadline AGNs are detected in X-rays, and these are among the most luminous X-ray sources in the GSS. Only one narrowline AGN is X-ray detected. Of the variable nuclei galaxies within the X-ray survey, 27% are X-ray detected. We find that 1.9% ± 0.6% of GSS galaxies to V gal = 24 are broad-line AGNs, 1.4% ± 0.5% are narrow-line AGNs, and 4.5% ± 1.4% contain variable nuclei. The fraction of spectroscopically identified BLAGNs and NLAGNs at z ∼ 1 reveals a marginally significant increase of 1.3% ± 0.9% when compared to the local population.

Original languageEnglish (US)
Pages (from-to)69-88
Number of pages20
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - Sep 2006
Externally publishedYes


  • Galaxies: active
  • Surveys

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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