NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-16 T10:05:11 PDT
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For refcode 2005MNRAS.358..131G:
Retrieve 31 NED objects in this reference.
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NED Abstract

Copyright by Royal Astronomical Society. 2005MNRAS.358..131G X-ray bright optically inactive galaxies in XMM-Newton/Sloan Digital Sky Survey fields: more diluted than absorbed? Georgantopoulos, I.; Georgakakis, A. Abstract. We explore the properties of X-ray bright optically inactive galaxies (XBONGs) detected in the 0.5-8 keV spectral band in 20 public XMM-Newton fields overlapping with the Sloan Digital Sky Survey (SDSS). We constrain our sample to optically extended systems with logf_X_/f_opt_ > -2 that have spectroscopic identifications available from the SDSS (r < 19.2 mag). The resulting sample contains 12 objects with L_X_(0.5-8 keV) = 5 x 10^41^-2 x 10^44^ erg s^-1^ in the redshift range 0.06 < z < 0.45. The X-ray emission in four cases is extended, suggesting the presence of hot gas associated with a cluster or group of galaxies. The X-ray spectral fits show that two additional sources are best fit with a thermal component emission (kT~ 1 keV). Three sources are most likely associated with active galactic nuclei (AGNs): their X-ray spectrum is described by a steep photon index {GAMMA}~ 1.9 typical of unobscured AGNs, while they are very luminous in X-rays [L_X_(0.5-8 keV) ~ 10^43^-10^44^ erg s^-1^]. Finally, three more sources could be associated with either normal galaxies or unobscured low-luminosity AGNs (L_X_ < 10^42^ erg s^-1^). We find no evidence for significant X-ray absorbing columns in any of our XBONGs. The above suggest that XBONGs, selected in the total 0.5-8 keV band, comprise a mixed bag of objects primarily including normal elliptical galaxies and type 1 AGNs whose optical nuclear spectrum is probably diluted by the strong stellar continuum. Nevertheless, as our sample is not statistically complete we cannot exclude the possibility that a fraction of optically fainter XBONGs may be associated with heavily obscured AGNs. Keywords: galaxies: active, quasars: general, X-rays: general
Retrieve 31 NED objects in this reference.
Please click here for ADS abstract

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