2MASS is a ground-based, near-infrared survey of the whole sky. It began
operations in the mid-1990's and completed observations in early 2001.
The final source catalogs and image Atlas was released to the public in
the fall of 2002
(Cutri et al 2000).
2MASS is fundamentally an imaging
survey, with detection and source characterization derived from images that
span the near-infrared windows: J (1.2 µm), H (1.6
µm), and Ks (2.2 µm).
The images were acquired using an efficient drift scan and freeze-frame
technique, painting the sky with 8.5' × 6° tiles or "scans"
(Skrutskie et al 1997),
forming 23 separate images per tile per near-infrared band of size 512
× 1024
pixels with resampled 1 arcsec pixels. A total of 4,121,439 FITS images
cover 4
steradians of the
sky. These images, 8.5' × 17' in angular size, are also
known as "coadds" since they are comprised of ~ 6 optimally dithered
samples per pixel. The effective beam or PSF FWHM is ~ 2 to 3",
depending on the atmospheric seeing, and is roughly the same for each
band. The typical 1-sigma
background noise is 21.4, 20.6, and 20.0 mag arcsec-2 for J,
H and Ks,
respectively. The images include a photometric zero-point calibration that
is accurate to 2-3% and an astrometric solution that is
accurate to < 0.2 arcsec
(Cutri et al 2000).
Stars and galaxies are detected and characterized from the 2MASS images. The Point Source Catalog (PSC) contains ~ 500 million objects, largely comprised of stars from the Milky Way. The Extended Source Catalog (XSC) contains ~ 1.6 million objects clearly resolved by 2MASS, chiefly comprised of extragalactic sources in the local Universe. This paper will focus on these resolved galaxies. The images and source catalogs are available to the public via the Infrared Science Archive (IRSA) and NASA Extragalactic Database (NED) of IPAC.