¹³ CO Observations Towards the 2^nd Galactic Quadrant Made with the Bordeaux Telescope

Abstract

A ¹³CO survey has been carried out in the 2^nd galactic quadrant. The emission is expected to be fainter here than in the first quadrant, because it originates outside the molecular ring; but it is also expected to be easier to interpret because there is neither distance ambiguity nor line overlap. Indeed the region ℓ = 108°–128°, already surveyed in ¹²CO by Cohen et al. (1980) consists of two main spiral features, the Perseus and Orion arms, and the Lindblad local ring, all of which are well separated either in radial velocity or in latitude. The Perseus arm is near v = −50 km s⁻¹; the Orion arm is near 0 km s⁻¹. Due to its smaller optical thickness, the ¹³CO molecule yields a better estimate of column densities than the existing ¹²CO observations, and allows discrimination between several small clouds that often appear blended in the same CO feature.