... (VLA

The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation.

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... (APS

The APS databases are supported by the National Science Foundation, the National Aeronautics and Space Administration, and the University of Minnesota, and are available at http://aps.umn.edu/.

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... field

We display only the region within the 1150$\times$1550 pixel image from which sources actually enter the catalog; sources closer to the boundaries will be extracted from the adjacent coadded images.

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... doubles

Note this number is different from that in Figure 15 because the latter includes only isolated doubles so as to examine as cleanly as possible the optical coincidence rates.

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