Column density maps for MWISP ^13^CO mol. clouds

We have obtained column density maps for an unbiased sample of 120 molecular clouds in the third quadrant of the Milky Way midplane (b<=|5|{deg}) within the Galactic longitude range from 195{deg} to 225{deg}, using the high-sensitivity ^12^CO and ^13^CO (J=1-0) data from the Milky Way Imaging Scroll Painting (MWISP) project. The probability density functions of the molecular hydrogen column density of the clouds, N-pdfs, are fitted with both a lognormal (LN) function and a lognormal plus power-law (LN+PL) function.

The molecular clouds are classified into three categories according to their shapes of N-pdfs, i.e., LN, LN+PL, and UN (unclear). About 72% of the molecular clouds fall into the LN category, while 18% and 10% fall into the LN+PL and UN categories, respectively. A PL scaling relation, {sigma}_s_{propto}N_H2_^0.44^, exists between the width of the N-pdf, {sigma}_s_, and the average column density, N_H2_, of the molecular clouds.