1996A&A...314..251H

The size-line width relation and the size-density relation are analysed for the molecular clouds from the CfA 1.2m telescope CO survey at high latitudes in the second quadrant. It is found that {DELTA}v∝r^0.5 and n∝r^–0.8, with correlation coefficient r=0.66 and r=-0.86, respectively. It is also shown that the virial mass is correlated to the CO luminosity, log(M_vir)=(0.78±0.09)log(L_CO)+(2.3±0.1). The size, line width, and radius for high latitude molecular clouds thus follow similar relations as found for giant molecular clouds. For the latter clouds these relations are usually interpreted as a consequence of virial equilibrium for clouds which are gravitational bound. It is shown that this interpretation is not valid for high latitude molecular clouds. The volume filling factor of molecular gas in high-latitude clouds is found to be rather low, less than 0.01. The pressure induced on the clouds by the surrounding H I gas is larger than the internal pressure induced by the motion of the molecular gas, indicating that the clouds are compressed by the external H I gas.