The 2MASS Extended Source Catalog (XSC) will include all resolved galaxies, regardless of their size, but will not accurately record the integrated flux for the largest galaxies due to their proximity to a "scan" edge. A typical 2MASS survey scan is 8.5 arcmin X 6 degrees, with 10% overlap between scans. Galaxies that are smaller than the overlap, D~50 arcsec, are guaranteed to be fully sampled in at least one survey scan. Larger galaxies may be truncated based on their proximity to a scan edge. Therefore we are constructing an atlas of large galaxies made from "pieces" of adjoining scans. (see for example the detailed construction of NGC 2903.) The atlas will consist of galaxies ranging in size from 2 to 30 arcmin, with a typical resolution of ~3 arcsec (w/ 1 arcsec pixels) in the 2MASS IR bands (J, H, Ks). The completed atlas provides the aggregate flux for each galaxy and a detailed view of the infrared morphology. At the completion of the 2MASS survey, the atlas will be fully available to the public and can be accessed through the NASA Extragalactic Database (NED).
The Large Galaxy Atlas will represent a valuable asset to the professional and amateur astronomical communities. The near-infrared forms a natural, complementary, bridge between the well-studied optical wavelengths (e.g., POSS and SDSS) and the longer (e.g., IRAS, ISO, NVSS, FIRST) wavelengths. The near-infrared is most sensitive to the older stellar populationsłthe dominant mass component in most galaxies. Hence, the Large Galaxy Atlas is an ideal data set to combine with imaging data at other wavelengths. It provides a clear contrast between the underlying mass component and, for example, star formation regions as seen in the optical or mid-infrared bands. In addition, the atlas will function as an astrometric "finding" chart/map for both professionals and amateurs searching for supernovae in galaxies.
As part of NASA's Origins Program, 2MASS is funded by NASA's Office of Space Science and the National Science Foundation. Results from 2MASS will benefit future Origins missions, including the Space Infrared Telescope Facility (SIRTF) and the Next Generation Space Telescope (NGSS). JPL manages the program for NASA's Office of Space Science, Washington, DC. JPL and IPAC are a division of the California Institute of Technology, Pasadena, CA.