The Five College Radio Astronomy Observatory CO Survey of the Outer Galaxy

Images from the FCRAO CO Survey of the Outer Galaxy and a description of the calibration and processing of the data are presented. The survey is comprised of 1,696,800 ¹²CO J = 1-0 spectra sampled every 50" between Galactic longitudes 102.49d and 141.54d and latitudes -3.03d and 5.41d. The V_LSR ranges from -153 to +40 km s^-1 sampled every 0.81 km s^-1 with a velocity resolution of 0.98 km s^-1. The survey provides the highest spatial dynamic range imaging of the molecular interstellar medium ever obtained. We describe the observing procedure and characterize the random and systematic noise of the survey.

The images reveal a wide diversity of spatial structure within the molecular interstellar medium. We identify several voids with angular extents of 2°-5° in diameter that may result from the cumulative interactions of ultraviolet radiation fields and stellar winds from newborn massive stars with ambient interstellar gas. It is demonstrated that a significant fraction of the integrated intensity summed over the survey field originates from regions with low peak antenna temperature and low column density assuming a conversion between integrated CO emission and molecular hydrogen column density. Assuming kinematic distances to the observed emission, we derive the radial profile of mass surface density and the variations of the z midplane and scale height of the molecular gas distribution with galactocentric radius.