Molecular gas in the Andromeda galaxy
  We present a new 12CO(J=1-0)-line survey of the Andromeda galaxy, M31, covering the bright disk with the highest resolution to date (85 pc along the major axis), observed On-the-Fly (in italics) with the IRAM 30-m telescope. We discuss the distribution of the CO emission and compare it with the distributions of HI and emission from cold dust traced at 175mum. Our main results are: 1. Most of the CO emission comes from the radial range R=3-16 kpc, but peaks near R=10 kpc. The emission is con- centrated in narrow, arm-like filaments defining two spiral arms with pitch angles of 7d-8d. The average arm-interarm brightness ratio along the western arms reaches 20 compared to 4 for HI. 2. For a constant conversion factor Xco, the molecular fraction of the neutral gas is enhanced in the arms and decreases radially. The apparent gas-to-dust ratios N(HI)/I175 and (N(HI)+2N(H2))/I175 increase by a factor of 20 between the centre and R=14 kpc, whereas the ratio 2N(H2)/I175 only increases by a factor of 4. Implications of these gradients are discussed. In the range R=8-14 kpc total gas and cold dust are well correlated; molecular gas is better correlated with cold dust than atomic gas. 
Ch. Nieten (1), N. Neininger (1,2,3), M. Guelin (3), H. Ungerechts   (4), R. Lucas (3), E. M. Berkhuijsen (1), R. Beck (1), ...