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Date and Time of the Query: 2019-04-21 T07:41:00 PDT
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For refcode 2006A&A...454...77L:
Retrieve 154 NED objects in this reference.
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2006A&A...454...77L Toward a clean sample of ultra-luminous X-ray sources M. Lopez-Corredoira; C. M. Gutierrez Received 19 December 2005 / Accepted 21 February 2006 Context. Observational follow-up programmes for the characterization of ultra-luminous X-ray sources (ULXs) require the construction of clean samples of such sources in which the contamination by foreground/background sources is minimum. Aims. We calculate the degree of foreground/background contaminants among the ULX sample candidates in a published catalogue and compare these computations with available spectroscopic identifications. Methods. We use statistics based on known densities of X-ray sources and AGN/QSOs selected in the optical. The analysis is done individually for each parent galaxy. The existing identifications of the optical counterparts are compiled from the literature. Results. More than a half of the ULXs, within twice the distance of the major axis of the 25 mag/arcsec^2^ isophote from RC3 nearby galaxies and with X-ray luminosities L_X_[2-10 keV ] >= 10^39^ erg/s, are expected to be high redshift background QSOs. A list of 25 objects (clean sample) confirmed to be real ULXs or to have a low probability of being contaminant foreground/background objects is provided. Key words: galaxies: statistics, galaxies: quasars: general
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