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In order to study the ISM and the interplay between the atomic and molecularcomponents in a low-metallicity environment, we present a complete high angularand spectral resolution map and data cube of the 12CO(2-1) emission from theLocal Group galaxy M33. Its metallicity is roughly half-solar, such that we cancompare its ISM with that of the Milky Way with the main changes being themetallicity and the gas mass fraction. The data have a 12" angular resolution(50pc) with a spectral resolution of 2.6 km/s and a mean noise level of 20 mKper channel in antenna temperature. A radial cut along the major axis was alsoobserved in the 12CO(1-0) line. The CO data cube and integrated intensity mapare optimal when using HI data to define the baseline window and the velocitiesover which the CO emission is integrated. Great care was taken when buildingthese maps, testing different windowing and baseline options and investigatingthe effect of error beam pickup. The total CO(2-1) luminosity is 2.8e7 K km/spc2, following the spiral arms in the inner disk. There is no clear variationin the CO(2-1/1-0) intensity ratio with radius and the average value is roughly0.8. The total molecular gas mass is estimated, using a N(H2)/Ico(1-0)=4e20cm-2/(K km/s) conversion factor, to be 3.1e8 Msol. The CO spectra in the cubewere shifted to zero velocity by subtracting the velocity of the HI peak fromthe CO spectra. Hence, the velocity dispersion between the atomic and molecularcomponents is extremely low, independently justifying the use of the HI line inbuilding our maps. Stacking the spectra in concentric rings shows that the COlinewidth and possibly the CO-HI velocity dispersion decrease in the outerdisk. Using the CO(2-1) emission to trace the molecular gas, the probabilitydistribution function of the H2 column density shows an excess at high columndensity above a log normal distribution.

The IRAM M33 CO(2-1) Survey - A complete census of the molecular gas out to 7 kpc