The X-ray observatories AXAF/Chandra and XMM/Newton have each identified several hundred X-ray sources in fields contained within the optical CDFS field of COMBO-17. The optical catalogue allows to identify likely counterparts at R<26, i.e. more than 80% of the X-ray sources. The classification provides photometric redshift data for the QSOs and the Sy-2-galaxies in the sample, but currently fails at the Sy-1-galaxies due to the lack of mixed templates, where contributions from both the host galaxy and its active nucleus are present in the spectrum.

In around one third of the sources, the X-ray position allows for more than one counterpart. Here, the classification can help to identify the most likely one, based on redshift and magnitude information. However, the optical data of COMBO-17 provide no clue for the presence of a Sy-2-AGN in a galaxy alone. So, for the ambiguous cases, we still have to rely on spectroscopy for the final identification of the optical counterpart. A proposal for such spectroscopy with VIMOS in Aug/Sep 2003 is led by J. Bergeron, Paris.

Contact person:  Christian Wolf, Oxford, and Günther Hasinger, Garching

Back to COMBO-17 science page