Sources in close proximity to large galaxies (selected from the LGA are identified and flagged in the XSC. Their photometry will be nulled in the final catalog. Proximity is defined to be the area enclosed by the "Kron" radius, whose elliptical shape is given by the "super" coadd position angle and axis ratio. The Kron radius is further scaled by 1.1 to capture all sources affected by the large galaxy. Extended sources that are with 5% of the nominal center of the galaxy (as given by the LGA galaxy position and Kron radius) are identified as "matches" with the LGA and are to be excised from the XSC.

Here are a few examples of the association identification.

Sources marked in green are extended sources that quality for XSC inclusion.
Sources marked in red are identifed as being located with the vicinity of an LGA galaxy; these sources will have their photometry nulled from the catalog.
Sources marked in white are LGA galaxy "matches" and will be deleted from the catalog.

M33

The nearby galaxy M33 has many resolved features, including stars and HII regions that are detected by 2MASS. See M33 mosaic for images of M33 from the LGA. The end result is a large amount of chaff in the XSC associated with M33. The following image shows M33 (in J-band) with extended sources marked in green, while red sources represent extended sources identified as being associated with M33. These sources will remain in the XSC, but will have their photometry nulled (since the background removal was not reliable for this large galaxy).

M33 and marked sources

White marked sources near the nucleus represent sources identified with the parent itself (M33 in this instance). These sources will be purged from the XSC (since they are replaced by the LGA parent source). Notice that the extended sources (red marked) are in fact pieces of the M33 spiral arms. Also notice that the distribution is asymmetric from north to south (many more sources detected in the south). The asymmetry arises from that fact that the m33 nucleus was nearly cut in half by a coadd boundary (with the "southern" coadd having the nucleus), so the background removal in the 2MASS pipeline (GALWORKS) was, likewise, non-uniform (each coadd had a separate solution for the background). This demonstrates another argument for eliminating these sources from the XSC (re: poor photometry and non-uniform detection).

M51

See M51 system mosaic for images of M51 from the LGA.