2MASS Extended Source Catalog: Overview and Algorithms

for submission to the Astronomical Journal The 2 Micron All-Sky Survey (2MASS) will observe over one-million galaxies and extended Galactic sources covering the entire sky at wavelengths between 1 and 2 pm. Most of these galaxies, from 70 to 8096, will be newly catalogued objects. The survey catalog will have both high completeness and reliability down to J = 15.0 and K, = 13.5 mag, or 1.7 mJy and 3.1 mJy, respectively. Galaxies as small as 10 ” are resolved and as large as-2.5 ’ are fully imaged. 2MASS will discover galaxies never seen before in the “zone of avoidance ” caused by the obscuring effects of Galactic dust and gas, limited only by the extreme number of stars near the Galactic center and at very low Galactic latitudes. The first public release of 2MASS data occurred in the Spring 1999, containing-2500 deg2 of northern hemisphere sky, including>75,000 extended sources. For each extended source we report an accurate position, size and shape, flux and surface brightness measures, 2-D image parameters, symmetry metrics (morphology proxies), and include a full resolution “postage stamp ” data cube containing the J, H and K, imaging data. This paper describes the basic algorithms used to detect and characterize extended sources in the 2MASS database and catalog. A future paper will provide a full statistical analysis and verification of the completeness, reliability and integrity of the first release catalog, as well as some of the basic scientific results of the catalog. 1