IRAM-PdB CO(1−0) rms map. The colour-coding corresponds to the noise level (σ_rms), corrected for the primary beam, of the map obtained at the IRAM-PdB. The blue cross indicates the (optical) centre of Andromeda (Crane et al. 1992). The red crosses correspond to the centre of the four fields observed at PdB with a half-power primary beam of 43.7′′ represented by red circles. The half-power beam is presented in the bottom left corner of the CO(1−0) observations.