T.H. Jarrett, T. Chester and R. Cutri (IPAC/Caltech/JPL)

S. Schneider and M. Skrutskie (UMASS)

J.P. Huchra (CfA/Harvard)

The 2 Micron All Sky Survey (2MASS) will observe over 1 million galaxies and extended Galactic sources covering the entire sky at wavelengths between 1 and 2 mm. Most of these galaxies, from 70 to 80%, will be newly catalogued objects. The survey catalog will have both high completeness and reliability down to J = 15.0 and K_s = 13.5 mag, or 1.7 mJy and 3.1 mJy, respectively. Galaxies as small as 10² are resolved and as large as ~2.5¢ are fully imaged. 2MASS discovers galaxies never seen before, revealing "zones" of sky traditionally avoided by astronomers due to the obscuring effects of Galactic dust and gas, limited by only the extreme number of stars near the Galactic center and adjoining plane of the Milky Way.

The first public release of 2MASS data is scheduled for the Spring of 1999, containing some 2500 deg² of northern hemisphere sky, including ~80,000 extended sources. For each extended source we report accurate positions, size and shape, integrated 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_s imaging data.

This document describes the algorithms used to detect and characterize extended sources, and outlines the resultant catalog content. We provide a full statistical analysis and verification of the completeness, reliability and integrity of the first release catalog. The basic content of this document will be submitted to the Astronomical Journal as a supplementary guide to the 2MASS Extended Source catalog.