Mapping of a Molecular Complex in a Northern Spiral Arm of M31.

A restricted CO map at high resolution (22") has been obtained with the IRAM 30 m telescope towards a North-East spiral arm of M31. We have detected sup 12 CO emission in 17 positions out of 41 observed. All the detected lines appear at the same LSR velocity, which implies that they come from a well-defined entity: a giant molecular complex. It has an H sub 2 mass of about 1.3X 10 sup 6 M(solar) and extends over roughly 160 pc. This complex is gravitationally bound; its structure is elongated and inhomogeneous on the 35 pc scale. A second velocity component shows up when adding all the spectra; it was also present in a low-resolution (1.7') spectrum from AT&T Bell Laboratories.