Comparison of the Planck CO(1 → 0) maps with the high Galactic latitudes CO detections and non detections from MHHST00. Top: correlation between the CO detections in MHHST00 and the Planck Type 2 and Type 3 maps. The latter was first smoothed to 15′. Bottom: distribution of all Planck CO(1 → 0) maps (at 15′ resolution) at the non-detection positions of MHHST00. The width of the distribution is compatible with the noise in the maps. Differences with respect to the values in Table 3 can be explained by the inhomogeneities of the noise in the Planck maps.