IV. 2MASS Data Processing

5. Extended Source Identification and Photometry

a. The Extended Source Processor

Extended Source Confusion Flag: cc_flg

The XSC confusion flag, "cc_flg", indicates whether a source is identified as as artifact, associated with an artifact, associated with a large galaxy (a.k.a. "chaff"), derived from the Large Galaxy Atlas, or in fact an "inscan" duplicate. This flag is used to omit non-extended sources from the final catalog.

cc_flg = "C" or to "D"

DBMAPCOR identifies sources (point or extended) that are in close proximity to bright stars. Two flavors: "C" indicates that the source fell within the "halo" of a bright star; "D" indicates that the sources fell on top of a bright star diffraction source. These "sources" are treated as artifacts and eliminated from the final XSC.

The source is identified as an in-scan duplicate (coadd-to-coadd duplicates). Dupes are defined to be sources within 5" radial proximity. The dupe marked with "I" is the one closest to an in-scan coadd edge (and hence, least desirable of the dupe pair). These sources are eliminated from the final XSC.

These sources are visually identified as artifacts, or "false-positives" (non-extended sources that make it past the star-galaxy battery of discrimination tests). The vis identification for these sources is, for the most part, serendipitous, and not done in any uniform complete fashion. Hence, these sources remain in the final catalog even though we know they are bogus sources.

These sources are visually identified as artifacts using uniform and (sqp-query) complete samples collected from the extended source database. Several kinds of queries were carried out (see below), exploring the vast parameter space that "artifacts" occupy in the extended source database. Since the queries were uniform/complete and the vis identification is robust/reliable, these sources are eliminated from the final XSC.

These sources are associated with very large galaxies. They tend to be "chaff"-like, in that they are not discrete sources but are in fact pieces of the large parent galaxy (e.g., HII complex on a spiral arm). These sources tend not to have reliable photometry due to the poor coadd background removal that arises from the large parent galaxy itself. These sources are identified and their photometry nulled from the XSC. An explanation of large galaxies is given here.

These sources are large galaxies, whose positions and photometry are derived from the Large Galaxy Atlas. These sources replace the pipeline measured sources (see cc_flg="z" above) in the catalog.

[Last Updated: 2002 Jul 16; by T. Jarrett]