2004/07/14 by C. Vignali, D. M. Alexander, A. Comastri · 4 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2004.08231.x
7 pages, 3 figures, 2 tables, accepted for publication in MNRAS
arxiv created 2004/07/14 · openalex publication_date 2004/10/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Recently, Zakamska et al. selected 291 high-ionization narrow-emission-line active galactic nuclei (AGN) in the redshift range 0.3–0.83 from the Sloan Digital Sky Survey (SDSS) spectroscopic data. The sample includes both type 2 Seyfert galaxies and their higher-luminosity ‘cousins’, Type II quasar candidates. Here we present the results on the X-ray properties of 17 of these objects for which archival X-ray data (ROSAT and XMM–Newton) are available. Three sources have been significantly (≳6σ) detected, one being the most radio-loud source of the sample; its X-ray emission, possibly enhanced by jet emission, is consistent with the absence of absorption. Another source has ≈6σ detection in the ROSAT All-Sky Survey (RASS), possibly complex radio structure, and no evidence for strong X-ray absorption. For the third X-ray detection, the XMM–Newton spectrum indicates a column density of NH= 1.26+0.75−0.51× 1022 cm−2; this result, coupled with the 2–10 keV luminosity of ≈ 4 × 1044 erg s−1, makes this source a genuine Type II quasar. Using the [Oiii]λ5007 line luminosities, we estimated the intrinsic X-ray power of the AGN and found that ≳47 per cent of the observed sample shows indications of X-ray absorption, with column densities ≳1022 cm−2. This provides further evidence that a considerable fraction are obscured quasars. Support for our conclusions also comes from the very recent analysis of RASS data performed by Zakamska et al., who found five additional lower-significance (≈2.1σ–3.6σ) X-ray matches.