Processing SMA Data
1.2 m Telescopes

The 1.2 meter Millimeter-Wave Telescope at the CfA has been studying the distribution and properties of dense, star-forming molecular clouds in our Galaxy and its nearest neighbors for over three decades. The telescope was operated from a Columbia University rooftop overlooking the Manhattan skyline for over 10 years before being moved to the CfA in 1986. A twin instrument was constructed at Columbia and shipped to Cerro Tololo, Chile in 1982. Together, these two instruments have obtained what is by far the most extensive, uniform, and widely-used Galactic survey of interstellar carbon monoxide (CO), the best general tracer of the largely invisible molecular hydrogen that constitutes most of the mass in molecular clouds.

After preliminary Galactic surveys in the mid-1970's revealed the vast extent of CO emission on the sky, it became clear that even with the relatively large 8 arcmin beams of the 1.2 meter telescopes a sensitive, well-sampled survey of the entire Galaxy would require many years. For that reason, during the period 1979-1986, the telescopes carried out a series of "superbeam" CO surveys in which angular resolution was sacrificed for the sake of coverage and speed. Most of these studies were conducted at an effective angular resolution of 1/2°, achieved by stepping through a 4 x 4 grid of positions on the sky separated by 1/8° (slightly less than one beamwidth) during the accumulation of a single spectrum. These low-resolution surveys, in total comprising over 31,000 spectra and sampling nearly a fifth of the entire sky (~7700 sq-deg), were combined into the first complete CO survey of the Milky Way by Dame et al. (1987).

Even before the "superbeam" surveys were undertaken, the two telescopes began to survey the Galaxy and its nearest neighbors at several times higher angular resolution--typically every beamwidth, but sometimes half or twice that--and at 5-10 times higher sensitivity per solid angle. Such observations cover the entire Galactic plane over a 4-10 degree band in latitude, all large local clouds at higher latitude, as well as the Large Magellanic Cloud and M31. In Dame, Hartmann, & Thaddeus (2001) all of the full-resolution observations, a total of 488,000 spectra, were combined into a new composite CO survey of the Galaxy. The 1987 and 2001 composite surveys have been widely used for studies of star formation and Galactic structure, the two having been cited by over 2500 papers in the astronomical literature.

After completion of the 2001 survey, the CfA 1.2 m telescope continued mapping the sky to ever greater angles from the Galactic plane, eventually reaching the north Galactic pole and our southern declination limit of -17°. In Dame & Thaddeus (2022), all of this new data were combined with the 2001 survey to produce the first complete CO survey of the entire northern sky.

The Data

This archive contains essentially all of the data presented in the 2001 paper as raw, interpolated, and noise-suppressed v-l-b FITS cubes as well as lb, lv, and bv integrated images (jpg). Most of the 37 individual surveys listed in Table 1 of DHT01 are available (see Individual Surveys), as are larger, composite FITS cubes covering the entire Galaxy (see Compsite Surveys). An explanation of the noise-suppression technique used for the so-called moment-masked cubes is also available (see Moment Masking). Also included is the CO survey of the entire northern sky described in Dame & Thaddeus 2022 (see Northern Sky Survey).