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The HELLAS2XMM 1dF survey: on the nature of high X-ray to optical flux ratio sources

F. Fiore·M. Brusa·F. Cocchia·A. Baldi·N. Carangelo·P. Ciliegi·A. Comastri·F. La Franca·R. Maiolino·G. Matt·S. Molendi·M. Mignoli·G. C. Perola·P. Severgnini·C. Vignali
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Abstract

We present results from the photometric and spectroscopic identification of 122 X-ray sources discovered by XMM-Newton in the 2-10 keV band (the HELLAS2XMM 1dF sample). One of the most interesting results (which is found also in deeper sourveys) is that ~20% of the sources have an X-ray to optical flux ratio (X/O) ten times or more higher than that of optically selected AGN. Unlike the faint sources found in the ultra-deep Chandra and XMM-Newton surveys, which reach X-ray (and optical) fluxes >~10 times lower than in the HELLAS2XMM sample, many of the extreme X/O sources in our sample have R~25 and are therefore accessible to optical spectroscopy. We report the identification of 13 sources with extreme X/O values. While four of these sources are broad line QSO, eight of them are narrow line QSO, seemingly the extension to very high luminosity of the type 2 Seyfert galaxies.

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F. Fiore, M. Brusa, F. Cocchia, A. Baldi, N. Carangelo, P. Ciliegi, A. Comastri, F. La Franca, R. Maiolino, G. Matt, S. Molendi, M. Mignoli, G. C. Perola, P. Severgnini, C. Vignali. 2003-10-10. The HELLAS2XMM 1dF survey: on the nature of high X-ray to optical flux ratio sources. https://arxiv.org/abs/astro-ph/0310298

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