XMM source lists are to be matched with source lists from other instruments, including INT WFC, APMCAT and CIRSI. In this document, the matching of XMM lists with WFC data is described.
As the pipelines for processing XMM data are still being finalised, the XMM source lists used have varying formats, although this is expected to be resolved in the near future. In some cases systematic position offsets became apparent. These were corrected using an initial comparison with WFC data, after which the matching process was repeated. Some XMM source lists contained individual position errors, some not.
Both unmerged ( i.e. band by band) and merged WFC data was used. The matching was performed using merged source lists to enable, for example, colour--colour or colour magnitude plots of matched optical sources to be produced. However the likelihood ratio analysis presented below was performed using objects detected in the i--band only (usually the deepest, and also available for all fields for which any WFC data was available).
Quality control plots for WFC data can be found at the following location:
http://www.ast.cam.ac.uk/
xmmssc/xid/data_status.php
For each field, the small gif image in the `plots' column, if green, leads to the corresponding quality control plots. These are independent of any X--ray information and publicly accessible.