The High-Resolution OTF Survey of the 12CO in M 31

We are performing a fully sampled survey of the 12CO(1-0) line emission of the nearby galaxy M 31 with the IRAM 30-m telescope. The resolution obtained is 23" which corresponds to about 90 pc along the major axis. This small beam is well adapted to the size of typical structures of the molecular gas and allows to detect even interarm cloud complexes. We chose an on-the-fly observing technique which allows us to cover the large area of about 1 square degree in a reasonable time. Until now, almost three quarters of the galaxy have been observed in the (1-0) line and some selected regions with a longer integration time in the (2-1) transition as well. Compared to the HI emission, the spiral arms show a higher contrast and more structure, albeit the general morphology is very similar. A first analysis suggests that the CO emission is a very good tracer of the molecular gas in M 31. In addition to the survey, we perform observations of selected complexes down to the sub-arcsecond level with the IRAM interferometer. Together with data of other species such as dust or neutral carbon we hope to proceed towards a better understanding of the molecular gas at large and small scales.