科研之友
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摘要
We report a new sample of obscured active galactic nuclei (AGNs) selected from the XMM-Newton serendipitous source and AKARI point-source catalogs. We match X-ray sources with infrared (18 and 90 mu m) sources located at vertical bar b vertical bar > 10 degrees to create a sample consisting of 173 objects. Their optical classifications and absorption column densities measured by X-ray spectra are compiled and study efficient selection criteria to find obscured AGNs. We apply the criteria (1) X-ray hardness ratio defined by using the 2-4.5 keV and 4.5-12 keV bands > -0.1 and (2) EPIC-PN count rate (CR) in the 0.2-12 keV to infrared flux ratio CR/F-90 < 0.1 or CR/F-18 < 1, where F-18 and F-90 are infrared fluxes at 18 and 90 mu m in Jy, respectively, to search for obscured AGNs. X-ray spectra of 48 candidates, for which no X-ray results have been published, are analyzed and X-ray evidence for the presence of obscured AGNs such as a convex shape X-ray spectrum indicative of absorption of N-H similar to 10(22-24) cm(-2), a very flat continuum, or a strong Fe-K emission line with an equivalent width of > 700 eV is found in 26 objects. Six of. them are classified as Compton-thick AGNs, and four are represented by either Compton-thin or Compton-thick spectral models. The success rate of finding obscured AGNs combining our analysis and the literature is 92% if the 18 mu m condition is used. Of. the 26 objects, 4 are optically classified as an H II nucleus and are new "elusive AGNs" in which star formation activity likely overwhelms AGN emission in the optical and infrared bands.
- 出版日期2015-11-20
