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Title: XMM-Newton observations reveal AGN in apparently normal galaxies
Authors: Severgnini, P.
Caccianiga, A.
Braito, V.
Della Ceca, R.
Maccacaro, T.
Wolter, A.
Sekiguchi, K.
Sasaki, T.
Yoshida, M.
Akiyama, M.
Watson, Michael G.
Barcons, X.
Carrera, F.J.
Pietsch, W.
Webb, N.A.
First Published: Aug-2003
Publisher: EDP Sciences for European Southern Observatory (ESO)
Citation: Astronomy and Astrophysics, 2003, 406 (2), pp.483-492
Abstract: We have performed a detailed analysis of 3 optically normal galaxies extracted from the XMM Bright Serendipitous Source Sample. Thanks to the good statistics of the XMM-Newton data, we have unveiled the presence of an AGN in all of them. In particular, we detect both X-ray obscured ([superscript N][subscript H] > 10[superscript 22] cm[superscript -2]) and unobscured ([superscript N][subscript H] < 10[superscript 22] cm[superscript -2]) AGNs with intrinsic 2-10 keV luminosities in the range between 10[superscript 42]-10[superscript 43] erg s[superscript -1]. We find that the X-ray and optical properties of the sources discussed here could be explained assuming a standard AGN hosted by galaxies with magnitudes M[subscript R]< M *, taking properly into account the absorption associated with the AGN, the optical faintness of the nuclear emission with respect to the host galaxy, and the inadequate set-up and atmospheric conditions during the optical spectroscopic observations. Our new spectroscopic observations have revealed the expected AGN features also in the optical band. These results clearly show that optical spectroscopy sometimes can be inefficient in revealing the presence of an AGN, which instead is clearly found from an X-ray spectroscopic investigation. This remarks the importance of being careful in proposing the identification of X-ray sources (especially at faint fluxes) when only low quality optical spectra are in hand. This is particularly important for faint surveys (such as those with XMM-Newton and Chandra), in which optically dull but X-ray active objects are being found in sizeable numbers.
DOI Link: 10.1051/0004-6361:20030625
ISSN: 0004-6361
eISSN: 1432-0746
Version: Publisher Version
Status: Peer-reviewed
Type: Article
Rights: © ESO 2003. Reproduced with permission from Astronomy & Astrophysics.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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