A multi-wavelength survey of AGN in the XMM-LSS field. I. Quasar selection via the KX technique
Abstract
Aims: We present a sample of candidate quasars selected using the KX-technique. The data cover 0.68 deg2 of the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey area where overlapping multi-wavelength imaging data permits an investigation of the physical nature of selected sources.
Methods: The KX method identifies quasars on the basis of their optical (R and z') to near-infrared (K_s) photometry and point-like morphology. We combine these data with optical (u^*,g', r',i',z') and mid-infrared (3.6-24 μm) wavebands to reconstruct the spectral energy distributions (SEDs) of candidate quasars.
Results: Of 93 sources selected as candidate quasars by the KX method, 25 are classified as quasars by the subsequent SED analysis. Spectroscopic observations are available for 12/25 of these sources and confirm the quasar hypothesis in each case. Even more, 90% of the SED-classified quasars show X-ray emission, a property not shared by any of the false candidates in the KX-selected sample. Applying a photometric redshift analysis to the sources without spectroscopy indicates that the 25 sources classified as quasars occupy the interval 0.7 ≤ z ≤ 2.5. The remaining 68/93 sources are classified as stars and unresolved galaxies.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- February 2009
- DOI:
- 10.1051/0004-6361:200809584
- arXiv:
- arXiv:0812.3588
- Bibcode:
- 2009A&A...494..579N
- Keywords:
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- techniques: photometric;
- galaxies: aquasars: general;
- galaxies: active;
- Astrophysics
- E-Print:
- 13 pages, 9 figures, A&