期刊
ASTROPHYSICAL JOURNAL
卷 736, 期 1, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/736/1/28
关键词
galaxies: active; galaxies: nuclei; quasars: emission lines; X-rays: galaxies
资金
- Chandra X-ray Center [GO0-11010X]
- NASA ADP [NNX10AC99G]
- NSERC
- Alfred P. Sloan Foundation
- National Science Foundation
- U.S. Department of Energy
- National Aeronautics and Space Administration
- Japanese Monbukagakusho
- Max Planck Society
- Higher Education Funding Council for England
We report the results from Chandra and XMM-Newton observations of a sample of 10 type 1 quasars selected to have unusual UV emission-line properties (weak and blueshifted high-ionization lines; strong UV Fe emission) similar to those of PHL 1811, a confirmed intrinsically X-ray weak quasar. These quasars were identified by the Sloan Digital Sky Survey at high redshift (z approximate to 2.2); eight are radio quiet while two are radio intermediate. All of the radio-quiet PHL 1811 analogs, without exception, are notably X-ray weak by a mean factor of approximate to 13. These sources lack broad absorption lines and have blue UV/optical continua, supporting the hypothesis that they are intrinsically X-ray weak like PHL 1811 itself. However, their average X-ray spectrum appears to be harder than those of typical quasars, which may indicate the presence of heavy intrinsic X-ray absorption. Our sample of radio-quiet PHL 1811 analogs supports a connection between an X-ray weak spectral energy distribution and PHL 1811-like UV emission lines; this connection provides an economical way to identify X-ray weak type 1 quasars. The fraction of radio-quiet PHL 1811 analogs in the radio-quiet quasar population is estimated to be less than or similar to 1.2%. We have investigated correlations between relative X-ray brightness and UV emission-line properties (e. g., C IV equivalent width and blueshift) for a sample combining our radio-quiet PHL 1811 analogs, PHL 1811 itself, and typical type 1 quasars. These correlation analyses suggest that PHL 1811 analogs may have extreme wind-dominated broad emission-line regions. Observationally, the radio-quiet PHL 1811 analogs appear to be a subset (approximate to 30%) of radio-quiet weak-line quasars (WLQs). The existence of a subset of quasars in which high-ionization shielding gas covers most of the broad emission-line region (BELR), but little more than the BELR, could potentially unify the PHL 1811 analogs and WLQs. The two radio-intermediate PHL 1811 analogs are X-ray bright. X-ray spectral analyses and consideration of their multiwavelength properties suggest that one of them has jet-dominated X-ray emission, while the nature of the other remains unclear.
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