By 1994 Infrared detector technology had made such huge advances in the previous decade that the only existing near-infrared sky survey (TMASS Neugebauer & Leighton 1969) no longer served as a useful context within which to interpret observations or select sources for study. The University of Massachusetts therefore lead a new project, called the Two Micron All Sky Survey (2MASS), which canvassed the entire sky for stars and galaxies with a sensitivity 50,000 times greater than that of the previous TMASS.
The scientific motivation for obtaining a new, deep view of the sky in the near-infrared rested on the following advantages:
- In the near-infrared, the extinction of the interstellar medium is only ~10% of that at optical wavelengths. Thus, it is possible to see clearly through the Milky Way to distances that are significatly larger than those accessible optically. It is also possible to detect galaxies without the hindrance of the optical "Zone of Avoidance" or of dust in the galaxies themselves.
- The
evolved red giants which
produce most of
the light of other galaxies are brightest in the near-infrared.
Furthermore, these stars have evolved from those which are most common
in other galaxies, namely low-mass stars. Therefore a census of
galaxies in the near-infrared is optimally sensitive to the stellar
mass.
A
comparison
of a portion of the galactic plane at 0.43 µm, 0.65
µm, 2.17 µm, and 12 µm. - There are certain classes of objects -- e.g., brown dwarfs, stars which have too little mass to sustain nuclear burning -- which are expected to emit almost exclusively at near-infrared wavelengths. A census of these objects requires a deep, large-area survey. Surveys naturally detect the nearest, and thus brightest and most easily studied, examples of any class of object.
Michael Skrutskie led the 2MASS science team. UMASS was responsible for the overall management of the project, and for developing the infrared cameras, telescopes, and on-site computing systems. The data were processed at the Infrared Processing and Analysis Center at Caltech.
The Northern Hemisphere 2MASS facility at Mt. Hopkins began routine survey observations in June 1997. The Southern Hemisphere 2MASS facility at Cerro Tololo began routine survey operations in March 1998. Operations were completed in November 2001 at Mt. Hopkins and in February 2001 at Cerro Tololo.
The 2MASS All Sky Catalog was released to the public in June 2003.
- Two Matching 1.3m Telescopes, Optimized for Efficient Sky Coverage
- Sites are Mt. Hopkins and CTIO
- Cameras include 3 infrared arrays, 256 × 256 -- one for each the three bands ( J (1.25 µm), H (1.65 µm), and Ks (2.17 µm)
- Camera Pixel Size is 2.0" x 2.0"
- Tilting secondary motion during declination scanning freezes frames.
- 1.3 second exposure time per frame x 6 frames per source = 7.8s integration time.
- Sub-stepping in both the in-scan and cross-scan direction minimizes effects of undersampling due to large pixels.
- Mapping Rate of 70 sq. deg./band/night
The 2MASS project was funded by NASA and the National Science Foundation.